diff --git a/upb/def.c b/upb/def.c
index 4423053d3e..b3114cdeba 100644
--- a/upb/def.c
+++ b/upb/def.c
@@ -1337,6 +1337,7 @@ bool upb_fielddef_checkdescriptortype(int32_t type) {
 
 /* upb_msgdef *****************************************************************/
 
+static const char *kDurationFullMessageName = "google.protobuf.Duration";
 static const char *kTimestampFullMessageName = "google.protobuf.Timestamp";
 
 static void visitmsg(const upb_refcounted *r, upb_refcounted_visit *visit,
@@ -1595,6 +1596,10 @@ bool upb_msgdef_mapentry(const upb_msgdef *m) {
   return m->map_entry;
 }
 
+bool upb_msgdef_duration(const upb_msgdef *m) {
+  return strcmp(upb_msgdef_fullname(m), kDurationFullMessageName) == 0;
+}
+
 bool upb_msgdef_timestamp(const upb_msgdef *m) {
   return strcmp(upb_msgdef_fullname(m), kTimestampFullMessageName) == 0;
 }
diff --git a/upb/def.h b/upb/def.h
index b6d197951f..5b9e8e71b6 100644
--- a/upb/def.h
+++ b/upb/def.h
@@ -664,6 +664,10 @@ typedef upb_strtable_iter upb_msg_oneof_iter;
 #define UPB_MAPENTRY_VALUE 2
 
 /* Well-known field tag numbers for timestamp messages. */
+#define UPB_DURATION_SECONDS 1
+#define UPB_DURATION_NANOS 2
+
+/* Well-known field tag numbers for duration messages. */
 #define UPB_TIMESTAMP_SECONDS 1
 #define UPB_TIMESTAMP_NANOS 2
 
@@ -781,6 +785,9 @@ class upb::MessageDef {
   void setmapentry(bool map_entry);
   bool mapentry() const;
 
+  /* Is this message a duration? */
+  bool duration() const;
+
   /* Is this message a timestamp? */
   bool timestamp() const;
 
@@ -925,6 +932,7 @@ bool upb_msgdef_addoneof(upb_msgdef *m, upb_oneofdef *o, const void *ref_donor,
 bool upb_msgdef_setfullname(upb_msgdef *m, const char *fullname, upb_status *s);
 void upb_msgdef_setmapentry(upb_msgdef *m, bool map_entry);
 bool upb_msgdef_mapentry(const upb_msgdef *m);
+bool upb_msgdef_duration(const upb_msgdef *m);
 bool upb_msgdef_timestamp(const upb_msgdef *m);
 bool upb_msgdef_setsyntax(upb_msgdef *m, upb_syntax_t syntax);
 
@@ -1865,6 +1873,9 @@ inline void MessageDef::setmapentry(bool map_entry) {
 inline bool MessageDef::mapentry() const {
   return upb_msgdef_mapentry(this);
 }
+inline bool MessageDef::duration() const {
+  return upb_msgdef_duration(this);
+}
 inline bool MessageDef::timestamp() const {
   return upb_msgdef_timestamp(this);
 }
diff --git a/upb/json/parser.c b/upb/json/parser.c
index e5b0554ab8..81fdba88f5 100644
--- a/upb/json/parser.c
+++ b/upb/json/parser.c
@@ -64,6 +64,10 @@ static bool is_boolean_wrapper_object(upb_json_parser *p);
 static bool does_boolean_wrapper_start(upb_json_parser *p);
 static bool does_boolean_wrapper_end(upb_json_parser *p);
 
+static bool is_duration_object(upb_json_parser *p);
+static bool does_duration_start(upb_json_parser *p);
+static bool does_duration_end(upb_json_parser *p);
+
 static bool is_timestamp_object(upb_json_parser *p);
 static bool does_timestamp_start(upb_json_parser *p);
 static bool does_timestamp_end(upb_json_parser *p);
@@ -908,7 +912,7 @@ static bool start_stringval(upb_json_parser *p) {
   if (is_top_level(p)) {
     if (is_string_wrapper_object(p)) {
       start_wrapper_object(p);
-    } else if (is_timestamp_object(p)) {
+    } else if (is_timestamp_object(p) || is_duration_object(p)) {
       start_object(p);
     } else {
       return false;
@@ -918,7 +922,7 @@ static bool start_stringval(upb_json_parser *p) {
       return false;
     }
     start_wrapper_object(p);
-  } else if (does_timestamp_start(p)) {
+  } else if (does_timestamp_start(p) || does_duration_start(p)) {
     if (!start_subobject(p)) {
       return false;
     }
@@ -979,7 +983,7 @@ static bool start_stringval(upb_json_parser *p) {
 static bool end_stringval_nontop(upb_json_parser *p) {
   bool ok = true;
 
-  if (is_timestamp_object(p)) {
+  if (is_timestamp_object(p) || is_duration_object(p)) {
     multipart_end(p);
     return true;
   }
@@ -1060,7 +1064,7 @@ static bool end_stringval(upb_json_parser *p) {
     }
   }
 
-  if (does_timestamp_end(p)) {
+  if (does_timestamp_end(p) || does_duration_end(p)) {
     end_object(p);
     if (!is_top_level(p)) {
       end_subobject(p);
@@ -1070,6 +1074,103 @@ static bool end_stringval(upb_json_parser *p) {
   return true;
 }
 
+static void start_duration_base(upb_json_parser *p, const char *ptr) {
+  capture_begin(p, ptr);
+}
+
+static bool end_duration_base(upb_json_parser *p, const char *ptr) {
+  size_t len;
+  const char *buf;
+  char seconds_buf[14];
+  char nanos_buf[12];
+  char *end;
+  int64_t seconds = 0;
+  int32_t nanos = 0;
+  double val = 0.0;
+  const char *seconds_membername = "seconds";
+  const char *nanos_membername = "nanos";
+  size_t fraction_start;
+
+  if (!capture_end(p, ptr)) {
+    return false;
+  }
+
+  buf = accumulate_getptr(p, &len);
+
+  memset(seconds_buf, 0, 14);
+  memset(nanos_buf, 0, 12);
+
+  /* Find out base end. The maximus duration is 315576000000, which cannot be
+   * represented by double without losing precision. Thus, we need to handle
+   * fraction and base separately. */
+  for (fraction_start = 0; fraction_start < len && buf[fraction_start] != '.';
+       fraction_start++);
+
+  /* Parse base */
+  memcpy(seconds_buf, buf, fraction_start);
+  seconds = strtol(seconds_buf, &end, 10);
+  if (errno == ERANGE || end != seconds_buf + fraction_start) {
+    upb_status_seterrf(&p->status, "error parsing duration: %s",
+                       seconds_buf);
+    upb_env_reporterror(p->env, &p->status);
+    return false;
+  }
+
+  if (seconds > 315576000000) {
+    upb_status_seterrf(&p->status, "error parsing duration: "
+                                   "maximum acceptable value is "
+                                   "315576000000");
+    upb_env_reporterror(p->env, &p->status);
+    return false;
+  }
+
+  if (seconds < -315576000000) {
+    upb_status_seterrf(&p->status, "error parsing duration: "
+                                   "minimum acceptable value is "
+                                   "-315576000000");
+    upb_env_reporterror(p->env, &p->status);
+    return false;
+  }
+
+  /* Parse fraction */
+  nanos_buf[0] = '0';
+  memcpy(nanos_buf + 1, buf + fraction_start, len - fraction_start);
+  val = strtod(nanos_buf, &end);
+  if (errno == ERANGE || end != nanos_buf + len - fraction_start + 1) {
+    upb_status_seterrf(&p->status, "error parsing duration: %s",
+                       nanos_buf);
+    upb_env_reporterror(p->env, &p->status);
+    return false;
+  }
+
+  nanos = val * 1000000000;
+  if (seconds < 0) nanos = -nanos;
+
+  /* Clean up buffer */
+  multipart_end(p);
+
+  /* Set seconds */
+  start_member(p);
+  capture_begin(p, seconds_membername);
+  capture_end(p, seconds_membername + 7);
+  end_membername(p);
+  upb_sink_putint64(&p->top->sink, parser_getsel(p), seconds);
+  end_member(p);
+
+  /* Set nanos */
+  start_member(p);
+  capture_begin(p, nanos_membername);
+  capture_end(p, nanos_membername + 5);
+  end_membername(p);
+  upb_sink_putint32(&p->top->sink, parser_getsel(p), nanos);
+  end_member(p);
+
+  /* Continue previous environment */
+  multipart_startaccum(p);
+
+  return true;
+}
+
 static void start_timestamp_base(upb_json_parser *p, const char *ptr) {
   capture_begin(p, ptr);
 }
@@ -1656,6 +1757,20 @@ static bool is_boolean_wrapper_object(upb_json_parser *p) {
   return p->top->m != NULL && is_bool_value(p->top->m);
 }
 
+static bool does_duration_start(upb_json_parser *p) {
+  return p->top->f != NULL &&
+         upb_fielddef_issubmsg(p->top->f) &&
+         upb_msgdef_duration(upb_fielddef_msgsubdef(p->top->f));
+}
+
+static bool does_duration_end(upb_json_parser *p) {
+  return p->top->m != NULL && upb_msgdef_duration(p->top->m);
+}
+
+static bool is_duration_object(upb_json_parser *p) {
+  return p->top->m != NULL && upb_msgdef_duration(p->top->m);
+}
+
 static bool does_timestamp_start(upb_json_parser *p) {
   return p->top->f != NULL &&
          upb_fielddef_issubmsg(p->top->f) &&
@@ -1691,26 +1806,27 @@ static bool is_timestamp_object(upb_json_parser *p) {
  * final state once, when the closing '"' is seen. */
 
 
-#line 1820 "upb/json/parser.rl"
+#line 1945 "upb/json/parser.rl"
 
 
 
-#line 1699 "upb/json/parser.c"
+#line 1814 "upb/json/parser.c"
 static const char _json_actions[] = {
 	0, 1, 0, 1, 1, 1, 3, 1, 
 	4, 1, 6, 1, 7, 1, 8, 1, 
-	9, 1, 10, 1, 18, 1, 20, 1, 
-	21, 1, 22, 1, 23, 1, 24, 1, 
-	25, 1, 27, 1, 29, 1, 30, 1, 
-	31, 1, 32, 1, 33, 1, 34, 1, 
-	35, 2, 4, 9, 2, 5, 6, 2, 
-	7, 3, 2, 7, 9, 2, 11, 12, 
-	2, 13, 14, 2, 15, 16, 2, 19, 
-	17, 2, 21, 23, 2, 22, 23, 2, 
-	26, 2, 2, 27, 35, 2, 28, 17, 
-	2, 30, 35, 2, 31, 35, 2, 32, 
-	35, 2, 34, 35, 3, 22, 19, 17, 
-	4, 11, 12, 13, 14
+	9, 1, 10, 1, 11, 1, 12, 1, 
+	13, 1, 21, 1, 23, 1, 24, 1, 
+	25, 1, 26, 1, 27, 1, 28, 1, 
+	30, 1, 32, 1, 33, 1, 34, 1, 
+	35, 1, 36, 1, 37, 1, 38, 2, 
+	4, 9, 2, 5, 6, 2, 7, 3, 
+	2, 7, 9, 2, 14, 15, 2, 16, 
+	17, 2, 18, 19, 2, 22, 20, 2, 
+	24, 26, 2, 25, 26, 2, 29, 2, 
+	2, 30, 38, 2, 31, 20, 2, 33, 
+	38, 2, 34, 38, 2, 35, 38, 2, 
+	37, 38, 3, 25, 22, 20, 4, 14, 
+	15, 16, 17
 };
 
 static const short _json_key_offsets[] = {
@@ -1719,15 +1835,16 @@ static const short _json_key_offsets[] = {
 	38, 43, 48, 49, 53, 58, 63, 68, 
 	72, 76, 79, 82, 84, 88, 92, 94, 
 	96, 101, 103, 105, 114, 120, 126, 132, 
-	138, 140, 142, 144, 146, 148, 149, 151, 
-	153, 154, 156, 158, 159, 161, 163, 164, 
-	166, 168, 169, 171, 173, 177, 179, 181, 
-	182, 183, 184, 185, 187, 192, 201, 202, 
-	202, 202, 207, 212, 217, 218, 219, 220, 
-	221, 221, 222, 223, 224, 224, 225, 226, 
-	227, 227, 232, 237, 238, 242, 247, 252, 
-	257, 261, 261, 264, 267, 270, 273, 276, 
-	279, 279, 279, 279
+	138, 140, 144, 147, 149, 151, 154, 155, 
+	159, 161, 163, 165, 167, 168, 170, 172, 
+	173, 175, 177, 178, 180, 182, 183, 185, 
+	187, 188, 190, 192, 196, 198, 200, 201, 
+	202, 203, 204, 206, 211, 220, 221, 221, 
+	221, 226, 231, 236, 237, 238, 239, 240, 
+	240, 241, 242, 243, 243, 244, 245, 246, 
+	246, 251, 256, 257, 261, 266, 271, 276, 
+	280, 280, 283, 286, 289, 292, 295, 298, 
+	298, 298, 298, 298
 };
 
 static const char _json_trans_keys[] = {
@@ -1748,24 +1865,27 @@ static const char _json_trans_keys[] = {
 	116, 117, 48, 57, 65, 70, 97, 102, 
 	48, 57, 65, 70, 97, 102, 48, 57, 
 	65, 70, 97, 102, 48, 57, 65, 70, 
-	97, 102, 34, 92, 48, 57, 48, 57, 
+	97, 102, 34, 92, 45, 48, 49, 57, 
+	48, 49, 57, 46, 115, 48, 57, 115, 
+	48, 57, 34, 46, 115, 48, 57, 48, 
+	57, 48, 57, 48, 57, 48, 57, 45, 
 	48, 57, 48, 57, 45, 48, 57, 48, 
-	57, 45, 48, 57, 48, 57, 84, 48, 
+	57, 84, 48, 57, 48, 57, 58, 48, 
 	57, 48, 57, 58, 48, 57, 48, 57, 
-	58, 48, 57, 48, 57, 43, 45, 46, 
-	90, 48, 57, 48, 57, 58, 48, 48, 
-	34, 48, 57, 43, 45, 90, 48, 57, 
-	34, 45, 91, 102, 110, 116, 123, 48, 
-	57, 34, 32, 93, 125, 9, 13, 32, 
-	44, 93, 9, 13, 32, 93, 125, 9, 
-	13, 97, 108, 115, 101, 117, 108, 108, 
-	114, 117, 101, 32, 34, 125, 9, 13, 
-	32, 34, 125, 9, 13, 34, 32, 58, 
-	9, 13, 32, 93, 125, 9, 13, 32, 
-	44, 125, 9, 13, 32, 44, 125, 9, 
-	13, 32, 34, 9, 13, 32, 9, 13, 
+	43, 45, 46, 90, 48, 57, 48, 57, 
+	58, 48, 48, 34, 48, 57, 43, 45, 
+	90, 48, 57, 34, 45, 91, 102, 110, 
+	116, 123, 48, 57, 34, 32, 93, 125, 
+	9, 13, 32, 44, 93, 9, 13, 32, 
+	93, 125, 9, 13, 97, 108, 115, 101, 
+	117, 108, 108, 114, 117, 101, 32, 34, 
+	125, 9, 13, 32, 34, 125, 9, 13, 
+	34, 32, 58, 9, 13, 32, 93, 125, 
+	9, 13, 32, 44, 125, 9, 13, 32, 
+	44, 125, 9, 13, 32, 34, 9, 13, 
 	32, 9, 13, 32, 9, 13, 32, 9, 
-	13, 32, 9, 13, 32, 9, 13, 0
+	13, 32, 9, 13, 32, 9, 13, 32, 
+	9, 13, 0
 };
 
 static const char _json_single_lengths[] = {
@@ -1774,14 +1894,15 @@ static const char _json_single_lengths[] = {
 	3, 3, 1, 2, 3, 3, 3, 2, 
 	2, 1, 3, 0, 2, 2, 0, 0, 
 	3, 2, 2, 9, 0, 0, 0, 0, 
-	2, 0, 0, 0, 0, 1, 0, 0, 
-	1, 0, 0, 1, 0, 0, 1, 0, 
-	0, 1, 0, 0, 4, 0, 0, 1, 
-	1, 1, 1, 0, 3, 7, 1, 0, 
-	0, 3, 3, 3, 1, 1, 1, 1, 
-	0, 1, 1, 1, 0, 1, 1, 1, 
-	0, 3, 3, 1, 2, 3, 3, 3, 
-	2, 0, 1, 1, 1, 1, 1, 1, 
+	2, 2, 1, 2, 0, 1, 1, 2, 
+	0, 0, 0, 0, 1, 0, 0, 1, 
+	0, 0, 1, 0, 0, 1, 0, 0, 
+	1, 0, 0, 4, 0, 0, 1, 1, 
+	1, 1, 0, 3, 7, 1, 0, 0, 
+	3, 3, 3, 1, 1, 1, 1, 0, 
+	1, 1, 1, 0, 1, 1, 1, 0, 
+	3, 3, 1, 2, 3, 3, 3, 2, 
+	0, 1, 1, 1, 1, 1, 1, 0, 
 	0, 0, 0, 0
 };
 
@@ -1791,14 +1912,15 @@ static const char _json_range_lengths[] = {
 	1, 1, 0, 1, 1, 1, 1, 1, 
 	1, 1, 0, 1, 1, 1, 1, 1, 
 	1, 0, 0, 0, 3, 3, 3, 3, 
-	0, 1, 1, 1, 1, 0, 1, 1, 
 	0, 1, 1, 0, 1, 1, 0, 1, 
-	1, 0, 1, 1, 0, 1, 1, 0, 
-	0, 0, 0, 1, 1, 1, 0, 0, 
-	0, 1, 1, 1, 0, 0, 0, 0, 
+	1, 1, 1, 1, 0, 1, 1, 0, 
+	1, 1, 0, 1, 1, 0, 1, 1, 
+	0, 1, 1, 0, 1, 1, 0, 0, 
+	0, 0, 1, 1, 1, 0, 0, 0, 
+	1, 1, 1, 0, 0, 0, 0, 0, 
 	0, 0, 0, 0, 0, 0, 0, 0, 
-	0, 1, 1, 0, 1, 1, 1, 1, 
-	1, 0, 1, 1, 1, 1, 1, 1, 
+	1, 1, 0, 1, 1, 1, 1, 1, 
+	0, 1, 1, 1, 1, 1, 1, 0, 
 	0, 0, 0, 0
 };
 
@@ -1808,15 +1930,16 @@ static const short _json_index_offsets[] = {
 	48, 53, 58, 60, 64, 69, 74, 79, 
 	83, 87, 90, 94, 96, 100, 104, 106, 
 	108, 113, 116, 119, 129, 133, 137, 141, 
-	145, 148, 150, 152, 154, 156, 158, 160, 
-	162, 164, 166, 168, 170, 172, 174, 176, 
-	178, 180, 182, 184, 186, 191, 193, 195, 
-	197, 199, 201, 203, 205, 210, 219, 221, 
-	222, 223, 228, 233, 238, 240, 242, 244, 
-	246, 247, 249, 251, 253, 254, 256, 258, 
-	260, 261, 266, 271, 273, 277, 282, 287, 
-	292, 296, 297, 300, 303, 306, 309, 312, 
-	315, 316, 317, 318
+	145, 148, 152, 155, 158, 160, 163, 165, 
+	169, 171, 173, 175, 177, 179, 181, 183, 
+	185, 187, 189, 191, 193, 195, 197, 199, 
+	201, 203, 205, 207, 212, 214, 216, 218, 
+	220, 222, 224, 226, 231, 240, 242, 243, 
+	244, 249, 254, 259, 261, 263, 265, 267, 
+	268, 270, 272, 274, 275, 277, 279, 281, 
+	282, 287, 292, 294, 298, 303, 308, 313, 
+	317, 318, 321, 324, 327, 330, 333, 336, 
+	337, 338, 339, 340
 };
 
 static const unsigned char _json_indicies[] = {
@@ -1838,72 +1961,77 @@ static const unsigned char _json_indicies[] = {
 	55, 55, 55, 55, 55, 55, 55, 56, 
 	1, 57, 57, 57, 1, 58, 58, 58, 
 	1, 59, 59, 59, 1, 60, 60, 60, 
-	1, 62, 63, 61, 64, 1, 65, 1, 
-	66, 1, 67, 1, 68, 1, 69, 1, 
-	70, 1, 71, 1, 72, 1, 73, 1, 
-	74, 1, 75, 1, 76, 1, 77, 1, 
-	78, 1, 79, 1, 80, 1, 81, 1, 
-	82, 1, 83, 83, 84, 85, 1, 86, 
-	1, 87, 1, 88, 1, 89, 1, 90, 
-	1, 91, 1, 92, 1, 93, 93, 94, 
-	92, 1, 95, 96, 97, 98, 99, 100, 
-	101, 96, 1, 102, 1, 103, 104, 106, 
-	107, 1, 106, 105, 108, 109, 107, 108, 
-	1, 109, 1, 1, 109, 105, 110, 1, 
-	111, 1, 112, 1, 113, 1, 114, 115, 
-	1, 116, 1, 117, 1, 118, 119, 1, 
-	120, 1, 121, 1, 122, 123, 124, 125, 
-	123, 1, 126, 127, 128, 126, 1, 129, 
-	1, 130, 131, 130, 1, 131, 1, 1, 
-	131, 132, 133, 134, 135, 133, 1, 136, 
-	137, 128, 136, 1, 137, 127, 137, 1, 
-	138, 139, 139, 1, 140, 140, 1, 141, 
-	141, 1, 142, 142, 1, 143, 143, 1, 
-	144, 144, 1, 1, 1, 1, 1, 0
+	1, 62, 63, 61, 64, 65, 66, 1, 
+	67, 68, 1, 69, 70, 1, 71, 1, 
+	70, 71, 1, 72, 1, 69, 70, 68, 
+	1, 73, 1, 74, 1, 75, 1, 76, 
+	1, 77, 1, 78, 1, 79, 1, 80, 
+	1, 81, 1, 82, 1, 83, 1, 84, 
+	1, 85, 1, 86, 1, 87, 1, 88, 
+	1, 89, 1, 90, 1, 91, 1, 92, 
+	92, 93, 94, 1, 95, 1, 96, 1, 
+	97, 1, 98, 1, 99, 1, 100, 1, 
+	101, 1, 102, 102, 103, 101, 1, 104, 
+	105, 106, 107, 108, 109, 110, 105, 1, 
+	111, 1, 112, 113, 115, 116, 1, 115, 
+	114, 117, 118, 116, 117, 1, 118, 1, 
+	1, 118, 114, 119, 1, 120, 1, 121, 
+	1, 122, 1, 123, 124, 1, 125, 1, 
+	126, 1, 127, 128, 1, 129, 1, 130, 
+	1, 131, 132, 133, 134, 132, 1, 135, 
+	136, 137, 135, 1, 138, 1, 139, 140, 
+	139, 1, 140, 1, 1, 140, 141, 142, 
+	143, 144, 142, 1, 145, 146, 137, 145, 
+	1, 146, 136, 146, 1, 147, 148, 148, 
+	1, 149, 149, 1, 150, 150, 1, 151, 
+	151, 1, 152, 152, 1, 153, 153, 1, 
+	1, 1, 1, 1, 1, 0
 };
 
 static const char _json_trans_targs[] = {
-	1, 0, 2, 99, 3, 6, 10, 13, 
-	16, 98, 4, 3, 98, 4, 5, 7, 
-	8, 9, 100, 11, 12, 101, 14, 15, 
-	102, 17, 18, 103, 17, 18, 103, 19, 
-	19, 20, 21, 22, 23, 103, 22, 23, 
-	25, 26, 32, 104, 27, 29, 28, 30, 
-	31, 34, 105, 35, 34, 105, 35, 33, 
-	36, 37, 38, 39, 40, 34, 105, 35, 
-	42, 43, 44, 45, 46, 47, 48, 49, 
-	50, 51, 52, 53, 54, 55, 56, 57, 
-	58, 59, 60, 61, 67, 66, 62, 63, 
-	64, 65, 66, 106, 68, 61, 66, 70, 
-	72, 73, 76, 81, 85, 89, 71, 107, 
-	107, 74, 73, 71, 74, 75, 77, 78, 
-	79, 80, 107, 82, 83, 84, 107, 86, 
-	87, 88, 107, 90, 91, 97, 90, 91, 
-	97, 92, 92, 93, 94, 95, 96, 97, 
-	95, 96, 107, 98, 98, 98, 98, 98, 
-	98
+	1, 0, 2, 106, 3, 6, 10, 13, 
+	16, 105, 4, 3, 105, 4, 5, 7, 
+	8, 9, 107, 11, 12, 108, 14, 15, 
+	109, 17, 18, 110, 17, 18, 110, 19, 
+	19, 20, 21, 22, 23, 110, 22, 23, 
+	25, 26, 32, 111, 27, 29, 28, 30, 
+	31, 34, 112, 35, 34, 112, 35, 33, 
+	36, 37, 38, 39, 40, 34, 112, 35, 
+	42, 43, 47, 43, 47, 44, 46, 45, 
+	113, 49, 50, 51, 52, 53, 54, 55, 
+	56, 57, 58, 59, 60, 61, 62, 63, 
+	64, 65, 66, 67, 68, 74, 73, 69, 
+	70, 71, 72, 73, 114, 75, 68, 73, 
+	77, 79, 80, 83, 88, 92, 96, 78, 
+	115, 115, 81, 80, 78, 81, 82, 84, 
+	85, 86, 87, 115, 89, 90, 91, 115, 
+	93, 94, 95, 115, 97, 98, 104, 97, 
+	98, 104, 99, 99, 100, 101, 102, 103, 
+	104, 102, 103, 115, 105, 105, 105, 105, 
+	105, 105
 };
 
 static const char _json_trans_actions[] = {
-	0, 0, 85, 79, 29, 0, 0, 0, 
-	43, 35, 19, 0, 31, 0, 0, 0, 
+	0, 0, 91, 85, 35, 0, 0, 0, 
+	49, 41, 25, 0, 37, 0, 0, 0, 
 	0, 0, 0, 0, 0, 0, 0, 0, 
-	0, 25, 100, 76, 0, 70, 27, 21, 
-	0, 0, 19, 23, 23, 73, 0, 0, 
+	0, 31, 106, 82, 0, 76, 33, 27, 
+	0, 0, 25, 29, 29, 79, 0, 0, 
 	0, 0, 0, 3, 0, 0, 0, 0, 
-	0, 5, 15, 0, 0, 49, 7, 13, 
-	0, 52, 9, 9, 9, 55, 58, 11, 
-	17, 0, 0, 0, 0, 0, 0, 0, 
+	0, 5, 15, 0, 0, 55, 7, 13, 
+	0, 58, 9, 9, 9, 61, 64, 11, 
+	17, 17, 17, 0, 0, 0, 19, 0, 
+	21, 23, 0, 0, 0, 0, 0, 0, 
 	0, 0, 0, 0, 0, 0, 0, 0, 
-	0, 0, 0, 104, 61, 104, 0, 0, 
-	0, 0, 0, 67, 0, 64, 64, 85, 
-	79, 29, 0, 0, 0, 43, 35, 47, 
-	82, 19, 0, 31, 0, 0, 0, 0, 
-	0, 0, 91, 0, 0, 0, 94, 0, 
-	0, 0, 88, 25, 100, 76, 0, 70, 
-	27, 21, 0, 0, 19, 23, 23, 73, 
-	0, 0, 97, 0, 33, 39, 41, 37, 
-	45
+	0, 0, 0, 0, 110, 67, 110, 0, 
+	0, 0, 0, 0, 73, 0, 70, 70, 
+	91, 85, 35, 0, 0, 0, 49, 41, 
+	53, 88, 25, 0, 37, 0, 0, 0, 
+	0, 0, 0, 97, 0, 0, 0, 100, 
+	0, 0, 0, 94, 31, 106, 82, 0, 
+	76, 33, 27, 0, 0, 25, 29, 29, 
+	79, 0, 0, 103, 0, 39, 45, 47, 
+	43, 51
 };
 
 static const char _json_eof_actions[] = {
@@ -1919,7 +2047,8 @@ static const char _json_eof_actions[] = {
 	0, 0, 0, 0, 0, 0, 0, 0, 
 	0, 0, 0, 0, 0, 0, 0, 0, 
 	0, 0, 0, 0, 0, 0, 0, 0, 
-	0, 0, 0, 33, 39, 41, 37, 45, 
+	0, 0, 0, 0, 0, 0, 0, 0, 
+	0, 0, 39, 45, 47, 43, 51, 0, 
 	0, 0, 0, 0
 };
 
@@ -1927,12 +2056,13 @@ static const int json_start = 1;
 
 static const int json_en_number_machine = 24;
 static const int json_en_string_machine = 33;
-static const int json_en_timestamp_machine = 41;
-static const int json_en_value_machine = 69;
+static const int json_en_duration_machine = 41;
+static const int json_en_timestamp_machine = 48;
+static const int json_en_value_machine = 76;
 static const int json_en_main = 1;
 
 
-#line 1823 "upb/json/parser.rl"
+#line 1948 "upb/json/parser.rl"
 
 size_t parse(void *closure, const void *hd, const char *buf, size_t size,
              const upb_bufhandle *handle) {
@@ -1955,7 +2085,7 @@ size_t parse(void *closure, const void *hd, const char *buf, size_t size,
   capture_resume(parser, buf);
 
   
-#line 1959 "upb/json/parser.c"
+#line 2089 "upb/json/parser.c"
 	{
 	int _klen;
 	unsigned int _trans;
@@ -2030,152 +2160,166 @@ _match:
 		switch ( *_acts++ )
 		{
 	case 1:
-#line 1704 "upb/json/parser.rl"
+#line 1819 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 2:
-#line 1706 "upb/json/parser.rl"
+#line 1821 "upb/json/parser.rl"
 	{ p--; {stack[top++] = cs; cs = 24; goto _again;} }
 	break;
 	case 3:
-#line 1710 "upb/json/parser.rl"
+#line 1825 "upb/json/parser.rl"
 	{ start_text(parser, p); }
 	break;
 	case 4:
-#line 1711 "upb/json/parser.rl"
+#line 1826 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_text(parser, p)); }
 	break;
 	case 5:
-#line 1717 "upb/json/parser.rl"
+#line 1832 "upb/json/parser.rl"
 	{ start_hex(parser); }
 	break;
 	case 6:
-#line 1718 "upb/json/parser.rl"
+#line 1833 "upb/json/parser.rl"
 	{ hexdigit(parser, p); }
 	break;
 	case 7:
-#line 1719 "upb/json/parser.rl"
+#line 1834 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_hex(parser)); }
 	break;
 	case 8:
-#line 1725 "upb/json/parser.rl"
+#line 1840 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(escape(parser, p)); }
 	break;
 	case 9:
-#line 1731 "upb/json/parser.rl"
+#line 1846 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 10:
-#line 1743 "upb/json/parser.rl"
-	{ start_timestamp_base(parser, p); }
+#line 1858 "upb/json/parser.rl"
+	{ start_duration_base(parser, p); }
 	break;
 	case 11:
-#line 1744 "upb/json/parser.rl"
-	{ CHECK_RETURN_TOP(end_timestamp_base(parser, p)); }
+#line 1859 "upb/json/parser.rl"
+	{ CHECK_RETURN_TOP(end_duration_base(parser, p)); }
 	break;
 	case 12:
-#line 1746 "upb/json/parser.rl"
-	{ start_timestamp_fraction(parser, p); }
+#line 1861 "upb/json/parser.rl"
+	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 13:
-#line 1747 "upb/json/parser.rl"
-	{ CHECK_RETURN_TOP(end_timestamp_fraction(parser, p)); }
+#line 1866 "upb/json/parser.rl"
+	{ start_timestamp_base(parser, p); }
 	break;
 	case 14:
-#line 1749 "upb/json/parser.rl"
-	{ start_timestamp_zone(parser, p); }
+#line 1867 "upb/json/parser.rl"
+	{ CHECK_RETURN_TOP(end_timestamp_base(parser, p)); }
 	break;
 	case 15:
-#line 1750 "upb/json/parser.rl"
-	{ CHECK_RETURN_TOP(end_timestamp_zone(parser, p)); }
+#line 1869 "upb/json/parser.rl"
+	{ start_timestamp_fraction(parser, p); }
 	break;
 	case 16:
-#line 1752 "upb/json/parser.rl"
-	{ p--; {cs = stack[--top]; goto _again;} }
+#line 1870 "upb/json/parser.rl"
+	{ CHECK_RETURN_TOP(end_timestamp_fraction(parser, p)); }
 	break;
 	case 17:
-#line 1757 "upb/json/parser.rl"
+#line 1872 "upb/json/parser.rl"
+	{ start_timestamp_zone(parser, p); }
+	break;
+	case 18:
+#line 1873 "upb/json/parser.rl"
+	{ CHECK_RETURN_TOP(end_timestamp_zone(parser, p)); }
+	break;
+	case 19:
+#line 1875 "upb/json/parser.rl"
+	{ p--; {cs = stack[--top]; goto _again;} }
+	break;
+	case 20:
+#line 1880 "upb/json/parser.rl"
 	{
         if (is_timestamp_object(parser)) {
+          {stack[top++] = cs; cs = 48; goto _again;}
+        } else if (is_duration_object(parser)) {
           {stack[top++] = cs; cs = 41; goto _again;}
         } else {
           {stack[top++] = cs; cs = 33; goto _again;}
         }
       }
 	break;
-	case 18:
-#line 1766 "upb/json/parser.rl"
-	{ p--; {stack[top++] = cs; cs = 69; goto _again;} }
+	case 21:
+#line 1891 "upb/json/parser.rl"
+	{ p--; {stack[top++] = cs; cs = 76; goto _again;} }
 	break;
-	case 19:
-#line 1771 "upb/json/parser.rl"
+	case 22:
+#line 1896 "upb/json/parser.rl"
 	{ start_member(parser); }
 	break;
-	case 20:
-#line 1772 "upb/json/parser.rl"
+	case 23:
+#line 1897 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_membername(parser)); }
 	break;
-	case 21:
-#line 1775 "upb/json/parser.rl"
+	case 24:
+#line 1900 "upb/json/parser.rl"
 	{ end_member(parser); }
 	break;
-	case 22:
-#line 1781 "upb/json/parser.rl"
+	case 25:
+#line 1906 "upb/json/parser.rl"
 	{ start_object(parser); }
 	break;
-	case 23:
-#line 1784 "upb/json/parser.rl"
+	case 26:
+#line 1909 "upb/json/parser.rl"
 	{ end_object(parser); }
 	break;
-	case 24:
-#line 1790 "upb/json/parser.rl"
+	case 27:
+#line 1915 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_array(parser)); }
 	break;
-	case 25:
-#line 1794 "upb/json/parser.rl"
+	case 28:
+#line 1919 "upb/json/parser.rl"
 	{ end_array(parser); }
 	break;
-	case 26:
-#line 1799 "upb/json/parser.rl"
+	case 29:
+#line 1924 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_number(parser, p)); }
 	break;
-	case 27:
-#line 1800 "upb/json/parser.rl"
+	case 30:
+#line 1925 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_number(parser, p)); }
 	break;
-	case 28:
-#line 1802 "upb/json/parser.rl"
+	case 31:
+#line 1927 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_stringval(parser)); }
 	break;
-	case 29:
-#line 1803 "upb/json/parser.rl"
+	case 32:
+#line 1928 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_stringval(parser)); }
 	break;
-	case 30:
-#line 1805 "upb/json/parser.rl"
+	case 33:
+#line 1930 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, true)); }
 	break;
-	case 31:
-#line 1807 "upb/json/parser.rl"
+	case 34:
+#line 1932 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, false)); }
 	break;
-	case 32:
-#line 1809 "upb/json/parser.rl"
+	case 35:
+#line 1934 "upb/json/parser.rl"
 	{ /* null value */ }
 	break;
-	case 33:
-#line 1811 "upb/json/parser.rl"
+	case 36:
+#line 1936 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_subobject(parser)); }
 	break;
-	case 34:
-#line 1812 "upb/json/parser.rl"
+	case 37:
+#line 1937 "upb/json/parser.rl"
 	{ end_subobject(parser); }
 	break;
-	case 35:
-#line 1817 "upb/json/parser.rl"
+	case 38:
+#line 1942 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
-#line 2179 "upb/json/parser.c"
+#line 2323 "upb/json/parser.c"
 		}
 	}
 
@@ -2192,30 +2336,30 @@ _again:
 	while ( __nacts-- > 0 ) {
 		switch ( *__acts++ ) {
 	case 0:
-#line 1702 "upb/json/parser.rl"
+#line 1817 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
-	case 27:
-#line 1800 "upb/json/parser.rl"
+	case 30:
+#line 1925 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_number(parser, p)); }
 	break;
-	case 30:
-#line 1805 "upb/json/parser.rl"
+	case 33:
+#line 1930 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, true)); }
 	break;
-	case 31:
-#line 1807 "upb/json/parser.rl"
+	case 34:
+#line 1932 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, false)); }
 	break;
-	case 32:
-#line 1809 "upb/json/parser.rl"
+	case 35:
+#line 1934 "upb/json/parser.rl"
 	{ /* null value */ }
 	break;
-	case 34:
-#line 1812 "upb/json/parser.rl"
+	case 37:
+#line 1937 "upb/json/parser.rl"
 	{ end_subobject(parser); }
 	break;
-#line 2219 "upb/json/parser.c"
+#line 2363 "upb/json/parser.c"
 		}
 	}
 	}
@@ -2223,7 +2367,7 @@ _again:
 	_out: {}
 	}
 
-#line 1845 "upb/json/parser.rl"
+#line 1970 "upb/json/parser.rl"
 
   if (p != pe) {
     upb_status_seterrf(&parser->status, "Parse error at '%.*s'\n", pe - p, p);
@@ -2245,6 +2389,7 @@ bool end(void *closure, const void *hd) {
 
   /* Prevent compile warning on unused static constants. */
   UPB_UNUSED(json_start);
+  UPB_UNUSED(json_en_duration_machine);
   UPB_UNUSED(json_en_number_machine);
   UPB_UNUSED(json_en_string_machine);
   UPB_UNUSED(json_en_timestamp_machine);
@@ -2254,9 +2399,9 @@ bool end(void *closure, const void *hd) {
   parse(parser, hd, &eof_ch, 0, NULL);
 
   return parser->current_state >= 
-#line 2258 "upb/json/parser.c"
-98
-#line 1874 "upb/json/parser.rl"
+#line 2403 "upb/json/parser.c"
+105
+#line 2000 "upb/json/parser.rl"
 ;
 }
 
@@ -2271,13 +2416,13 @@ static void json_parser_reset(upb_json_parser *p) {
 
   /* Emit Ragel initialization of the parser. */
   
-#line 2275 "upb/json/parser.c"
+#line 2420 "upb/json/parser.c"
 	{
 	cs = json_start;
 	top = 0;
 	}
 
-#line 1888 "upb/json/parser.rl"
+#line 2014 "upb/json/parser.rl"
   p->current_state = cs;
   p->parser_top = top;
   accumulate_clear(p);
diff --git a/upb/json/parser.rl b/upb/json/parser.rl
index 2dfb5d376d..2681217094 100644
--- a/upb/json/parser.rl
+++ b/upb/json/parser.rl
@@ -62,6 +62,10 @@ static bool is_boolean_wrapper_object(upb_json_parser *p);
 static bool does_boolean_wrapper_start(upb_json_parser *p);
 static bool does_boolean_wrapper_end(upb_json_parser *p);
 
+static bool is_duration_object(upb_json_parser *p);
+static bool does_duration_start(upb_json_parser *p);
+static bool does_duration_end(upb_json_parser *p);
+
 static bool is_timestamp_object(upb_json_parser *p);
 static bool does_timestamp_start(upb_json_parser *p);
 static bool does_timestamp_end(upb_json_parser *p);
@@ -906,7 +910,7 @@ static bool start_stringval(upb_json_parser *p) {
   if (is_top_level(p)) {
     if (is_string_wrapper_object(p)) {
       start_wrapper_object(p);
-    } else if (is_timestamp_object(p)) {
+    } else if (is_timestamp_object(p) || is_duration_object(p)) {
       start_object(p);
     } else {
       return false;
@@ -916,7 +920,7 @@ static bool start_stringval(upb_json_parser *p) {
       return false;
     }
     start_wrapper_object(p);
-  } else if (does_timestamp_start(p)) {
+  } else if (does_timestamp_start(p) || does_duration_start(p)) {
     if (!start_subobject(p)) {
       return false;
     }
@@ -977,7 +981,7 @@ static bool start_stringval(upb_json_parser *p) {
 static bool end_stringval_nontop(upb_json_parser *p) {
   bool ok = true;
 
-  if (is_timestamp_object(p)) {
+  if (is_timestamp_object(p) || is_duration_object(p)) {
     multipart_end(p);
     return true;
   }
@@ -1058,7 +1062,7 @@ static bool end_stringval(upb_json_parser *p) {
     }
   }
 
-  if (does_timestamp_end(p)) {
+  if (does_timestamp_end(p) || does_duration_end(p)) {
     end_object(p);
     if (!is_top_level(p)) {
       end_subobject(p);
@@ -1068,6 +1072,103 @@ static bool end_stringval(upb_json_parser *p) {
   return true;
 }
 
+static void start_duration_base(upb_json_parser *p, const char *ptr) {
+  capture_begin(p, ptr);
+}
+
+static bool end_duration_base(upb_json_parser *p, const char *ptr) {
+  size_t len;
+  const char *buf;
+  char seconds_buf[14];
+  char nanos_buf[12];
+  char *end;
+  int64_t seconds = 0;
+  int32_t nanos = 0;
+  double val = 0.0;
+  const char *seconds_membername = "seconds";
+  const char *nanos_membername = "nanos";
+  size_t fraction_start;
+
+  if (!capture_end(p, ptr)) {
+    return false;
+  }
+
+  buf = accumulate_getptr(p, &len);
+
+  memset(seconds_buf, 0, 14);
+  memset(nanos_buf, 0, 12);
+
+  /* Find out base end. The maximus duration is 315576000000, which cannot be
+   * represented by double without losing precision. Thus, we need to handle
+   * fraction and base separately. */
+  for (fraction_start = 0; fraction_start < len && buf[fraction_start] != '.';
+       fraction_start++);
+
+  /* Parse base */
+  memcpy(seconds_buf, buf, fraction_start);
+  seconds = strtol(seconds_buf, &end, 10);
+  if (errno == ERANGE || end != seconds_buf + fraction_start) {
+    upb_status_seterrf(&p->status, "error parsing duration: %s",
+                       seconds_buf);
+    upb_env_reporterror(p->env, &p->status);
+    return false;
+  }
+
+  if (seconds > 315576000000) {
+    upb_status_seterrf(&p->status, "error parsing duration: "
+                                   "maximum acceptable value is "
+                                   "315576000000");
+    upb_env_reporterror(p->env, &p->status);
+    return false;
+  }
+
+  if (seconds < -315576000000) {
+    upb_status_seterrf(&p->status, "error parsing duration: "
+                                   "minimum acceptable value is "
+                                   "-315576000000");
+    upb_env_reporterror(p->env, &p->status);
+    return false;
+  }
+
+  /* Parse fraction */
+  nanos_buf[0] = '0';
+  memcpy(nanos_buf + 1, buf + fraction_start, len - fraction_start);
+  val = strtod(nanos_buf, &end);
+  if (errno == ERANGE || end != nanos_buf + len - fraction_start + 1) {
+    upb_status_seterrf(&p->status, "error parsing duration: %s",
+                       nanos_buf);
+    upb_env_reporterror(p->env, &p->status);
+    return false;
+  }
+
+  nanos = val * 1000000000;
+  if (seconds < 0) nanos = -nanos;
+
+  /* Clean up buffer */
+  multipart_end(p);
+
+  /* Set seconds */
+  start_member(p);
+  capture_begin(p, seconds_membername);
+  capture_end(p, seconds_membername + 7);
+  end_membername(p);
+  upb_sink_putint64(&p->top->sink, parser_getsel(p), seconds);
+  end_member(p);
+
+  /* Set nanos */
+  start_member(p);
+  capture_begin(p, nanos_membername);
+  capture_end(p, nanos_membername + 5);
+  end_membername(p);
+  upb_sink_putint32(&p->top->sink, parser_getsel(p), nanos);
+  end_member(p);
+
+  /* Continue previous environment */
+  multipart_startaccum(p);
+
+  return true;
+}
+
 static void start_timestamp_base(upb_json_parser *p, const char *ptr) {
   capture_begin(p, ptr);
 }
@@ -1654,6 +1755,20 @@ static bool is_boolean_wrapper_object(upb_json_parser *p) {
   return p->top->m != NULL && is_bool_value(p->top->m);
 }
 
+static bool does_duration_start(upb_json_parser *p) {
+  return p->top->f != NULL &&
+         upb_fielddef_issubmsg(p->top->f) &&
+         upb_msgdef_duration(upb_fielddef_msgsubdef(p->top->f));
+}
+
+static bool does_duration_end(upb_json_parser *p) {
+  return p->top->m != NULL && upb_msgdef_duration(p->top->m);
+}
+
+static bool is_duration_object(upb_json_parser *p) {
+  return p->top->m != NULL && upb_msgdef_duration(p->top->m);
+}
+
 static bool does_timestamp_start(upb_json_parser *p) {
   return p->top->f != NULL &&
          upb_fielddef_issubmsg(p->top->f) &&
@@ -1738,6 +1853,14 @@ static bool is_timestamp_object(upb_json_parser *p) {
   minute = digit digit;
   second = digit digit;
 
+  duration_machine :=
+    ("-"? integer decimal?)
+      >{ start_duration_base(parser, p); }
+      %{ CHECK_RETURN_TOP(end_duration_base(parser, p)); }
+    's"'
+      @{ fhold; fret; }
+    ;
+
   timestamp_machine :=
     (year "-" month "-" day "T" hour ":" minute ":" second)
       >{ start_timestamp_base(parser, p); }
@@ -1757,6 +1880,8 @@ static bool is_timestamp_object(upb_json_parser *p) {
       @{
         if (is_timestamp_object(parser)) {
           fcall timestamp_machine;
+        } else if (is_duration_object(parser)) {
+          fcall duration_machine;
         } else {
           fcall string_machine;
         }
@@ -1863,6 +1988,7 @@ bool end(void *closure, const void *hd) {
 
   /* Prevent compile warning on unused static constants. */
   UPB_UNUSED(json_start);
+  UPB_UNUSED(json_en_duration_machine);
   UPB_UNUSED(json_en_number_machine);
   UPB_UNUSED(json_en_string_machine);
   UPB_UNUSED(json_en_timestamp_machine);
diff --git a/upb/json/printer.c b/upb/json/printer.c
index 9c8949ec9f..a3803a1761 100644
--- a/upb/json/printer.c
+++ b/upb/json/printer.c
@@ -692,22 +692,91 @@ void printer_sethandlers_mapentry(const void *closure, bool preserve_fieldnames,
   upb_handlerattr_uninit(&empty_attr);
 }
 
-static bool puttimestamp_seconds(void *closure, const void *handler_data,
-                                 int64_t seconds) {
+static bool putseconds(void *closure, const void *handler_data,
+                       int64_t seconds) {
   upb_json_printer *p = closure;
   p->seconds = seconds;
   UPB_UNUSED(handler_data);
   return true;
 }
 
-static bool puttimestamp_nanos(void *closure, const void *handler_data,
-                               int32_t nanos) {
+static bool putnanos(void *closure, const void *handler_data,
+                     int32_t nanos) {
   upb_json_printer *p = closure;
   p->nanos = nanos;
   UPB_UNUSED(handler_data);
   return true;
 }
 
+static bool printer_startdurationmsg(void *closure, const void *handler_data) {
+  upb_json_printer *p = closure;
+  UPB_UNUSED(handler_data);
+  if (p->depth_ == 0) {
+    upb_bytessink_start(p->output_, 0, &p->subc_);
+  }
+  return true;
+}
+
+#define UPB_DURATION_MAX_JSON_LEN 23
+#define UPB_DURATION_MAX_NANO_LEN 9
+
+static bool printer_enddurationmsg(void *closure, const void *handler_data,
+                                   upb_status *s) {
+  upb_json_printer *p = closure;
+  char buffer[UPB_DURATION_MAX_JSON_LEN];
+  size_t base_len;
+  size_t curr;
+  size_t i;
+
+  memset(buffer, 0, UPB_DURATION_MAX_JSON_LEN);
+
+  if (p->seconds < -315576000000) {
+    upb_status_seterrf(s, "error parsing duration: "
+                          "minimum acceptable value is "
+                          "-315576000000");
+    return false;
+  }
+
+  if (p->seconds > 315576000000) {
+    upb_status_seterrf(s, "error serializing duration: "
+                          "maximum acceptable value is "
+                          "315576000000");
+    return false;
+  }
+
+  _upb_snprintf(buffer, sizeof(buffer), "%ld", (long)p->seconds);
+  base_len = strlen(buffer);
+
+  if (p->nanos != 0) {
+    char nanos_buffer[UPB_DURATION_MAX_NANO_LEN + 3];
+    _upb_snprintf(nanos_buffer, sizeof(nanos_buffer), "%.9f",
+                  p->nanos / 1000000000.0);
+    /* Remove trailing 0. */
+    for (i = UPB_DURATION_MAX_NANO_LEN + 2;
+         nanos_buffer[i] == '0'; i--) {
+      nanos_buffer[i] = 0;
+    }
+    strcpy(buffer + base_len, nanos_buffer + 1);
+  }
+
+  curr = strlen(buffer);
+  strcpy(buffer + curr, "s");
+
+  p->seconds = 0;
+  p->nanos = 0;
+
+  print_data(p, "\"", 1);
+  print_data(p, buffer, strlen(buffer));
+  print_data(p, "\"", 1);
+
+  if (p->depth_ == 0) {
+    upb_bytessink_end(p->output_);
+  }
+
+  UPB_UNUSED(handler_data);
+  return true;
+}
+
 static bool printer_starttimestampmsg(void *closure, const void *handler_data) {
   upb_json_printer *p = closure;
   UPB_UNUSED(handler_data);
@@ -783,6 +852,25 @@ static bool printer_endtimestampmsg(void *closure, const void *handler_data,
   return true;
 }
 
+/* Set up handlers for a duration submessage. */
+void printer_sethandlers_duration(const void *closure, upb_handlers *h) {
+  const upb_msgdef *md = upb_handlers_msgdef(h);
+
+  const upb_fielddef* seconds_field =
+      upb_msgdef_itof(md, UPB_DURATION_SECONDS);
+  const upb_fielddef* nanos_field =
+      upb_msgdef_itof(md, UPB_DURATION_NANOS);
+
+  upb_handlerattr empty_attr = UPB_HANDLERATTR_INITIALIZER;
+
+  upb_handlers_setstartmsg(h, printer_startdurationmsg, &empty_attr);
+  upb_handlers_setint64(h, seconds_field, putseconds, &empty_attr);
+  upb_handlers_setint32(h, nanos_field, putnanos, &empty_attr);
+  upb_handlers_setendmsg(h, printer_enddurationmsg, &empty_attr);
+
+  UPB_UNUSED(closure);
+}
+
 /* Set up handlers for a timestamp submessage. Instead of printing fields
  * separately, the json representation of timestamp follows RFC 3339 */
 void printer_sethandlers_timestamp(const void *closure, upb_handlers *h) {
@@ -796,8 +884,8 @@ void printer_sethandlers_timestamp(const void *closure, upb_handlers *h) {
   upb_handlerattr empty_attr = UPB_HANDLERATTR_INITIALIZER;
 
   upb_handlers_setstartmsg(h, printer_starttimestampmsg, &empty_attr);
-  upb_handlers_setint64(h, seconds_field, puttimestamp_seconds, &empty_attr);
-  upb_handlers_setint32(h, nanos_field, puttimestamp_nanos, &empty_attr);
+  upb_handlers_setint64(h, seconds_field, putseconds, &empty_attr);
+  upb_handlers_setint32(h, nanos_field, putnanos, &empty_attr);
   upb_handlers_setendmsg(h, printer_endtimestampmsg, &empty_attr);
 
   UPB_UNUSED(closure);
@@ -818,6 +906,11 @@ void printer_sethandlers(const void *closure, upb_handlers *h) {
     return;
   }
 
+  if (upb_msgdef_duration(md)) {
+    printer_sethandlers_duration(closure, h);
+    return;
+  }
+
   if (upb_msgdef_timestamp(md)) {
     printer_sethandlers_timestamp(closure, h);
     return;