diff --git a/upb/json/parser.c b/upb/json/parser.c
index 10242aa3a0..3ae4722377 100644
--- a/upb/json/parser.c
+++ b/upb/json/parser.c
@@ -113,6 +113,9 @@ typedef struct {
    * because |f| is the field in the *current* message (i.e., the map-entry
    * message itself), not the parent's field that leads to this map. */
   const upb_fielddef *mapfield;
+
+  /* True if the field to be parsed is unknown. */
+  bool is_unknown_field;
 } upb_jsonparser_frame;
 
 struct upb_json_parser {
@@ -918,6 +921,10 @@ static bool end_bool(upb_json_parser *p, bool val) {
     start_value_object(p, VALUE_BOOLVALUE);
   }
 
+  if (p->top->is_unknown_field) {
+    return true;
+  }
+
   if (!parser_putbool(p, val)) {
     return false;
   }
@@ -1024,6 +1031,7 @@ static bool start_stringval(upb_json_parser *p) {
     inner->name_table = NULL;
     inner->is_map = false;
     inner->is_mapentry = false;
+    inner->is_unknown_field = false;
     p->top = inner;
 
     if (upb_fielddef_type(p->top->f) == UPB_TYPE_STRING) {
@@ -1515,6 +1523,7 @@ static bool handle_mapentry(upb_json_parser *p) {
   inner->name_table = NULL;
   inner->mapfield = mapfield;
   inner->is_map = false;
+  inner->is_unknown_field = false;
 
   /* Don't set this to true *yet* -- we reuse parsing handlers below to push
    * the key field value to the sink, and these handlers will pop the frame
@@ -1545,6 +1554,8 @@ static bool end_membername(upb_json_parser *p) {
   UPB_ASSERT(!p->top->f);
 
   if (!p->top->m) {
+    p->top->is_unknown_field = true;
+    multipart_end(p);
     return true;
   }
 
@@ -1561,6 +1572,7 @@ static bool end_membername(upb_json_parser *p) {
 
       return true;
     } else if (p->ignore_json_unknown) {
+      p->top->is_unknown_field = true;
       multipart_end(p);
       return true;
     } else {
@@ -1592,10 +1604,11 @@ static void end_member(upb_json_parser *p) {
   }
 
   p->top->f = NULL;
+  p->top->is_unknown_field = false;
 }
 
 static bool start_subobject(upb_json_parser *p) {
-  if (p->top->f == NULL) {
+  if (p->top->is_unknown_field) {
     upb_jsonparser_frame *inner;
     if (!check_stack(p)) return false;
 
@@ -1604,6 +1617,7 @@ static bool start_subobject(upb_json_parser *p) {
     inner->f = NULL;
     inner->is_map = false;
     inner->is_mapentry = false;
+    inner->is_unknown_field = false;
     p->top = inner;
     return true;
   }
@@ -1625,6 +1639,7 @@ static bool start_subobject(upb_json_parser *p) {
     inner->f = NULL;
     inner->is_map = true;
     inner->is_mapentry = false;
+    inner->is_unknown_field = false;
     p->top = inner;
 
     return true;
@@ -1645,6 +1660,7 @@ static bool start_subobject(upb_json_parser *p) {
     inner->f = NULL;
     inner->is_map = false;
     inner->is_mapentry = false;
+    inner->is_unknown_field = false;
     p->top = inner;
 
     return true;
@@ -1744,7 +1760,18 @@ static bool start_array(upb_json_parser *p) {
     start_listvalue_object(p);
   }
 
-  UPB_ASSERT(p->top->f);
+  if (p->top->is_unknown_field) {
+    inner = p->top + 1;
+    inner->m = NULL;
+    inner->name_table = NULL;
+    inner->f = NULL;
+    inner->is_map = false;
+    inner->is_mapentry = false;
+    inner->is_unknown_field = true;
+    p->top = inner;
+
+    return true;
+  }
 
   if (!upb_fielddef_isseq(p->top->f)) {
     upb_status_seterrf(&p->status,
@@ -1764,6 +1791,7 @@ static bool start_array(upb_json_parser *p) {
   inner->f = p->top->f;
   inner->is_map = false;
   inner->is_mapentry = false;
+  inner->is_unknown_field = false;
   p->top = inner;
 
   return true;
@@ -1775,6 +1803,11 @@ static void end_array(upb_json_parser *p) {
   UPB_ASSERT(p->top > p->stack);
 
   p->top--;
+
+  if (p->top->is_unknown_field) {
+    return;
+  }
+
   sel = getsel_for_handlertype(p, UPB_HANDLER_ENDSEQ);
   upb_sink_endseq(&p->top->sink, sel);
 
@@ -1794,13 +1827,13 @@ static void end_array(upb_json_parser *p) {
 }
 
 static void start_object(upb_json_parser *p) {
-  if (!p->top->is_map) {
+  if (!p->top->is_map && p->top->m != NULL) {
     upb_sink_startmsg(&p->top->sink);
   }
 }
 
 static void end_object(upb_json_parser *p) {
-  if (!p->top->is_map) {
+  if (!p->top->is_map && p->top->m != NULL) {
     upb_status status;
     upb_status_clear(&status);
     upb_sink_endmsg(&p->top->sink, &status);
@@ -1912,7 +1945,7 @@ static void end_structvalue_object(upb_json_parser *p) {
 }
 
 static bool is_top_level(upb_json_parser *p) {
-  return p->top == p->stack && p->top->f == NULL;
+  return p->top == p->stack && p->top->f == NULL && !p->top->is_unknown_field;
 }
 
 static bool is_wellknown_msg(upb_json_parser *p, upb_wellknowntype_t type) {
@@ -1975,11 +2008,11 @@ static bool is_string_wrapper_object(upb_json_parser *p) {
  * final state once, when the closing '"' is seen. */
 
 
-#line 2114 "upb/json/parser.rl"
+#line 2147 "upb/json/parser.rl"
 
 
 
-#line 1983 "upb/json/parser.c"
+#line 2016 "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, 
@@ -2230,7 +2263,7 @@ static const int json_en_value_machine = 76;
 static const int json_en_main = 1;
 
 
-#line 2117 "upb/json/parser.rl"
+#line 2150 "upb/json/parser.rl"
 
 size_t parse(void *closure, const void *hd, const char *buf, size_t size,
              const upb_bufhandle *handle) {
@@ -2253,7 +2286,7 @@ size_t parse(void *closure, const void *hd, const char *buf, size_t size,
   capture_resume(parser, buf);
 
   
-#line 2257 "upb/json/parser.c"
+#line 2290 "upb/json/parser.c"
 	{
 	int _klen;
 	unsigned int _trans;
@@ -2328,83 +2361,83 @@ _match:
 		switch ( *_acts++ )
 		{
 	case 1:
-#line 1988 "upb/json/parser.rl"
+#line 2021 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 2:
-#line 1990 "upb/json/parser.rl"
+#line 2023 "upb/json/parser.rl"
 	{ p--; {stack[top++] = cs; cs = 24; goto _again;} }
 	break;
 	case 3:
-#line 1994 "upb/json/parser.rl"
+#line 2027 "upb/json/parser.rl"
 	{ start_text(parser, p); }
 	break;
 	case 4:
-#line 1995 "upb/json/parser.rl"
+#line 2028 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_text(parser, p)); }
 	break;
 	case 5:
-#line 2001 "upb/json/parser.rl"
+#line 2034 "upb/json/parser.rl"
 	{ start_hex(parser); }
 	break;
 	case 6:
-#line 2002 "upb/json/parser.rl"
+#line 2035 "upb/json/parser.rl"
 	{ hexdigit(parser, p); }
 	break;
 	case 7:
-#line 2003 "upb/json/parser.rl"
+#line 2036 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_hex(parser)); }
 	break;
 	case 8:
-#line 2009 "upb/json/parser.rl"
+#line 2042 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(escape(parser, p)); }
 	break;
 	case 9:
-#line 2015 "upb/json/parser.rl"
+#line 2048 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 10:
-#line 2027 "upb/json/parser.rl"
+#line 2060 "upb/json/parser.rl"
 	{ start_duration_base(parser, p); }
 	break;
 	case 11:
-#line 2028 "upb/json/parser.rl"
+#line 2061 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_duration_base(parser, p)); }
 	break;
 	case 12:
-#line 2030 "upb/json/parser.rl"
+#line 2063 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 13:
-#line 2035 "upb/json/parser.rl"
+#line 2068 "upb/json/parser.rl"
 	{ start_timestamp_base(parser, p); }
 	break;
 	case 14:
-#line 2036 "upb/json/parser.rl"
+#line 2069 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_timestamp_base(parser, p)); }
 	break;
 	case 15:
-#line 2038 "upb/json/parser.rl"
+#line 2071 "upb/json/parser.rl"
 	{ start_timestamp_fraction(parser, p); }
 	break;
 	case 16:
-#line 2039 "upb/json/parser.rl"
+#line 2072 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_timestamp_fraction(parser, p)); }
 	break;
 	case 17:
-#line 2041 "upb/json/parser.rl"
+#line 2074 "upb/json/parser.rl"
 	{ start_timestamp_zone(parser, p); }
 	break;
 	case 18:
-#line 2042 "upb/json/parser.rl"
+#line 2075 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_timestamp_zone(parser, p)); }
 	break;
 	case 19:
-#line 2044 "upb/json/parser.rl"
+#line 2077 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 20:
-#line 2049 "upb/json/parser.rl"
+#line 2082 "upb/json/parser.rl"
 	{
         if (is_wellknown_msg(parser, UPB_WELLKNOWN_TIMESTAMP)) {
           {stack[top++] = cs; cs = 48; goto _again;}
@@ -2416,78 +2449,78 @@ _match:
       }
 	break;
 	case 21:
-#line 2060 "upb/json/parser.rl"
+#line 2093 "upb/json/parser.rl"
 	{ p--; {stack[top++] = cs; cs = 76; goto _again;} }
 	break;
 	case 22:
-#line 2065 "upb/json/parser.rl"
+#line 2098 "upb/json/parser.rl"
 	{ start_member(parser); }
 	break;
 	case 23:
-#line 2066 "upb/json/parser.rl"
+#line 2099 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_membername(parser)); }
 	break;
 	case 24:
-#line 2069 "upb/json/parser.rl"
+#line 2102 "upb/json/parser.rl"
 	{ end_member(parser); }
 	break;
 	case 25:
-#line 2075 "upb/json/parser.rl"
+#line 2108 "upb/json/parser.rl"
 	{ start_object(parser); }
 	break;
 	case 26:
-#line 2078 "upb/json/parser.rl"
+#line 2111 "upb/json/parser.rl"
 	{ end_object(parser); }
 	break;
 	case 27:
-#line 2084 "upb/json/parser.rl"
+#line 2117 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_array(parser)); }
 	break;
 	case 28:
-#line 2088 "upb/json/parser.rl"
+#line 2121 "upb/json/parser.rl"
 	{ end_array(parser); }
 	break;
 	case 29:
-#line 2093 "upb/json/parser.rl"
+#line 2126 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_number(parser, p)); }
 	break;
 	case 30:
-#line 2094 "upb/json/parser.rl"
+#line 2127 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_number(parser, p)); }
 	break;
 	case 31:
-#line 2096 "upb/json/parser.rl"
+#line 2129 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_stringval(parser)); }
 	break;
 	case 32:
-#line 2097 "upb/json/parser.rl"
+#line 2130 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_stringval(parser)); }
 	break;
 	case 33:
-#line 2099 "upb/json/parser.rl"
+#line 2132 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, true)); }
 	break;
 	case 34:
-#line 2101 "upb/json/parser.rl"
+#line 2134 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, false)); }
 	break;
 	case 35:
-#line 2103 "upb/json/parser.rl"
+#line 2136 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_null(parser)); }
 	break;
 	case 36:
-#line 2105 "upb/json/parser.rl"
+#line 2138 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_subobject_full(parser)); }
 	break;
 	case 37:
-#line 2106 "upb/json/parser.rl"
+#line 2139 "upb/json/parser.rl"
 	{ end_subobject_full(parser); }
 	break;
 	case 38:
-#line 2111 "upb/json/parser.rl"
+#line 2144 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
-#line 2491 "upb/json/parser.c"
+#line 2524 "upb/json/parser.c"
 		}
 	}
 
@@ -2504,34 +2537,34 @@ _again:
 	while ( __nacts-- > 0 ) {
 		switch ( *__acts++ ) {
 	case 0:
-#line 1986 "upb/json/parser.rl"
+#line 2019 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 26:
-#line 2078 "upb/json/parser.rl"
+#line 2111 "upb/json/parser.rl"
 	{ end_object(parser); }
 	break;
 	case 30:
-#line 2094 "upb/json/parser.rl"
+#line 2127 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_number(parser, p)); }
 	break;
 	case 33:
-#line 2099 "upb/json/parser.rl"
+#line 2132 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, true)); }
 	break;
 	case 34:
-#line 2101 "upb/json/parser.rl"
+#line 2134 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, false)); }
 	break;
 	case 35:
-#line 2103 "upb/json/parser.rl"
+#line 2136 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_null(parser)); }
 	break;
 	case 37:
-#line 2106 "upb/json/parser.rl"
+#line 2139 "upb/json/parser.rl"
 	{ end_subobject_full(parser); }
 	break;
-#line 2535 "upb/json/parser.c"
+#line 2568 "upb/json/parser.c"
 		}
 	}
 	}
@@ -2539,7 +2572,7 @@ _again:
 	_out: {}
 	}
 
-#line 2139 "upb/json/parser.rl"
+#line 2172 "upb/json/parser.rl"
 
   if (p != pe) {
     upb_status_seterrf(&parser->status, "Parse error at '%.*s'\n", pe - p, p);
@@ -2571,9 +2604,9 @@ bool end(void *closure, const void *hd) {
   parse(parser, hd, &eof_ch, 0, NULL);
 
   return parser->current_state >= 
-#line 2575 "upb/json/parser.c"
+#line 2608 "upb/json/parser.c"
 105
-#line 2169 "upb/json/parser.rl"
+#line 2202 "upb/json/parser.rl"
 ;
 }
 
@@ -2585,16 +2618,17 @@ static void json_parser_reset(upb_json_parser *p) {
   p->top->f = NULL;
   p->top->is_map = false;
   p->top->is_mapentry = false;
+  p->top->is_unknown_field = false;
 
   /* Emit Ragel initialization of the parser. */
   
-#line 2592 "upb/json/parser.c"
+#line 2626 "upb/json/parser.c"
 	{
 	cs = json_start;
 	top = 0;
 	}
 
-#line 2183 "upb/json/parser.rl"
+#line 2217 "upb/json/parser.rl"
   p->current_state = cs;
   p->parser_top = top;
   accumulate_clear(p);
diff --git a/upb/json/parser.h b/upb/json/parser.h
index 316df0873d..15beaeb987 100644
--- a/upb/json/parser.h
+++ b/upb/json/parser.h
@@ -29,7 +29,7 @@ UPB_DECLARE_DERIVED_TYPE(upb::json::ParserMethod, upb::RefCounted,
  * constructed.  This hint may be an overestimate for some build configurations.
  * But if the parser library is upgraded without recompiling the application,
  * it may be an underestimate. */
-#define UPB_JSON_PARSER_SIZE 4160
+#define UPB_JSON_PARSER_SIZE 4672
 
 #ifdef __cplusplus
 
diff --git a/upb/json/parser.rl b/upb/json/parser.rl
index 8e6caa970e..29efd09dae 100644
--- a/upb/json/parser.rl
+++ b/upb/json/parser.rl
@@ -111,6 +111,9 @@ typedef struct {
    * because |f| is the field in the *current* message (i.e., the map-entry
    * message itself), not the parent's field that leads to this map. */
   const upb_fielddef *mapfield;
+
+  /* True if the field to be parsed is unknown. */
+  bool is_unknown_field;
 } upb_jsonparser_frame;
 
 struct upb_json_parser {
@@ -916,6 +919,10 @@ static bool end_bool(upb_json_parser *p, bool val) {
     start_value_object(p, VALUE_BOOLVALUE);
   }
 
+  if (p->top->is_unknown_field) {
+    return true;
+  }
+
   if (!parser_putbool(p, val)) {
     return false;
   }
@@ -1022,6 +1029,7 @@ static bool start_stringval(upb_json_parser *p) {
     inner->name_table = NULL;
     inner->is_map = false;
     inner->is_mapentry = false;
+    inner->is_unknown_field = false;
     p->top = inner;
 
     if (upb_fielddef_type(p->top->f) == UPB_TYPE_STRING) {
@@ -1513,6 +1521,7 @@ static bool handle_mapentry(upb_json_parser *p) {
   inner->name_table = NULL;
   inner->mapfield = mapfield;
   inner->is_map = false;
+  inner->is_unknown_field = false;
 
   /* Don't set this to true *yet* -- we reuse parsing handlers below to push
    * the key field value to the sink, and these handlers will pop the frame
@@ -1543,6 +1552,8 @@ static bool end_membername(upb_json_parser *p) {
   UPB_ASSERT(!p->top->f);
 
   if (!p->top->m) {
+    p->top->is_unknown_field = true;
+    multipart_end(p);
     return true;
   }
 
@@ -1559,6 +1570,7 @@ static bool end_membername(upb_json_parser *p) {
 
       return true;
     } else if (p->ignore_json_unknown) {
+      p->top->is_unknown_field = true;
       multipart_end(p);
       return true;
     } else {
@@ -1590,10 +1602,11 @@ static void end_member(upb_json_parser *p) {
   }
 
   p->top->f = NULL;
+  p->top->is_unknown_field = false;
 }
 
 static bool start_subobject(upb_json_parser *p) {
-  if (p->top->f == NULL) {
+  if (p->top->is_unknown_field) {
     upb_jsonparser_frame *inner;
     if (!check_stack(p)) return false;
 
@@ -1602,6 +1615,7 @@ static bool start_subobject(upb_json_parser *p) {
     inner->f = NULL;
     inner->is_map = false;
     inner->is_mapentry = false;
+    inner->is_unknown_field = false;
     p->top = inner;
     return true;
   }
@@ -1623,6 +1637,7 @@ static bool start_subobject(upb_json_parser *p) {
     inner->f = NULL;
     inner->is_map = true;
     inner->is_mapentry = false;
+    inner->is_unknown_field = false;
     p->top = inner;
 
     return true;
@@ -1643,6 +1658,7 @@ static bool start_subobject(upb_json_parser *p) {
     inner->f = NULL;
     inner->is_map = false;
     inner->is_mapentry = false;
+    inner->is_unknown_field = false;
     p->top = inner;
 
     return true;
@@ -1742,7 +1758,18 @@ static bool start_array(upb_json_parser *p) {
     start_listvalue_object(p);
   }
 
-  UPB_ASSERT(p->top->f);
+  if (p->top->is_unknown_field) {
+    inner = p->top + 1;
+    inner->m = NULL;
+    inner->name_table = NULL;
+    inner->f = NULL;
+    inner->is_map = false;
+    inner->is_mapentry = false;
+    inner->is_unknown_field = true;
+    p->top = inner;
+
+    return true;
+  }
 
   if (!upb_fielddef_isseq(p->top->f)) {
     upb_status_seterrf(&p->status,
@@ -1762,6 +1789,7 @@ static bool start_array(upb_json_parser *p) {
   inner->f = p->top->f;
   inner->is_map = false;
   inner->is_mapentry = false;
+  inner->is_unknown_field = false;
   p->top = inner;
 
   return true;
@@ -1773,6 +1801,11 @@ static void end_array(upb_json_parser *p) {
   UPB_ASSERT(p->top > p->stack);
 
   p->top--;
+
+  if (p->top->is_unknown_field) {
+    return;
+  }
+
   sel = getsel_for_handlertype(p, UPB_HANDLER_ENDSEQ);
   upb_sink_endseq(&p->top->sink, sel);
 
@@ -1792,13 +1825,13 @@ static void end_array(upb_json_parser *p) {
 }
 
 static void start_object(upb_json_parser *p) {
-  if (!p->top->is_map) {
+  if (!p->top->is_map && p->top->m != NULL) {
     upb_sink_startmsg(&p->top->sink);
   }
 }
 
 static void end_object(upb_json_parser *p) {
-  if (!p->top->is_map) {
+  if (!p->top->is_map && p->top->m != NULL) {
     upb_status status;
     upb_status_clear(&status);
     upb_sink_endmsg(&p->top->sink, &status);
@@ -1910,7 +1943,7 @@ static void end_structvalue_object(upb_json_parser *p) {
 }
 
 static bool is_top_level(upb_json_parser *p) {
-  return p->top == p->stack && p->top->f == NULL;
+  return p->top == p->stack && p->top->f == NULL && !p->top->is_unknown_field;
 }
 
 static bool is_wellknown_msg(upb_json_parser *p, upb_wellknowntype_t type) {
@@ -2177,6 +2210,7 @@ static void json_parser_reset(upb_json_parser *p) {
   p->top->f = NULL;
   p->top->is_map = false;
   p->top->is_mapentry = false;
+  p->top->is_unknown_field = false;
 
   /* Emit Ragel initialization of the parser. */
   %% write init;