diff --git a/tools/amalgamate.py b/tools/amalgamate.py
index 374d126ec0..5545af5a20 100755
--- a/tools/amalgamate.py
+++ b/tools/amalgamate.py
@@ -17,6 +17,7 @@ class Amalgamator:
     self.output_c = open(output_path + "upb.c", "w")
 
     self.output_c.write("/* Amalgamated source file */\n")
+    self.output_c.write('#define _XOPEN_SOURCE 700\n')
     self.output_c.write('#include "upb.h"\n')
     self.output_c.write(open("upb/port_def.inc").read())
 
diff --git a/upb/json/parser.c b/upb/json/parser.c
index 0b9eb92ac3..f73533ace8 100644
--- a/upb/json/parser.c
+++ b/upb/json/parser.c
@@ -21,6 +21,9 @@
 ** - handling of keys/escape-sequences/etc that span input buffers.
 */
 
+/* Need to define _XOPEN_SOURCE before any include to make strptime work. */
+#define _XOPEN_SOURCE 700
+
 #include <ctype.h>
 #include <errno.h>
 #include <float.h>
@@ -30,10 +33,6 @@
 #include <stdlib.h>
 #include <string.h>
 
-/* Need to define __USE_XOPEN before including time.h to make strptime work. */
-#ifndef __USE_XOPEN
-#define __USE_XOPEN
-#endif
 #include <time.h>
 
 #include "upb/json/parser.h"
@@ -1537,11 +1536,18 @@ static bool end_timestamp_base(upb_json_parser *p, const char *ptr) {
   memcpy(timestamp_buf + UPB_TIMESTAMP_BASE_SIZE, "GMT", 3);
   timestamp_buf[UPB_TIMESTAMP_BASE_SIZE + 3] = 0;
 
+#if defined __MINGW32__ || defined __MINGW64__
+  upb_status_seterrf(
+      &p->status, "error parsing timestamp: mingw doesn't support strptime");
+  upb_env_reporterror(p->env, &p->status);
+  return false;
+#else
   /* Parse seconds */
   if (strptime(timestamp_buf, "%FT%H:%M:%S%Z", &p->tm) == NULL) {
     upb_status_seterrf(p->status, "error parsing timestamp: %s", buf);
     return false;
   }
+#endif
 
   /* Clean up buffer */
   multipart_end(p);
@@ -2508,11 +2514,11 @@ static bool does_fieldmask_end(upb_json_parser *p) {
  * final state once, when the closing '"' is seen. */
 
 
-#line 2690 "upb/json/parser.rl"
+#line 2696 "upb/json/parser.rl"
 
 
 
-#line 2516 "upb/json/parser.c"
+#line 2522 "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, 
@@ -2764,7 +2770,7 @@ static const int json_en_value_machine = 78;
 static const int json_en_main = 1;
 
 
-#line 2693 "upb/json/parser.rl"
+#line 2699 "upb/json/parser.rl"
 
 size_t parse(void *closure, const void *hd, const char *buf, size_t size,
              const upb_bufhandle *handle) {
@@ -2787,7 +2793,7 @@ size_t parse(void *closure, const void *hd, const char *buf, size_t size,
   capture_resume(parser, buf);
 
   
-#line 2791 "upb/json/parser.c"
+#line 2797 "upb/json/parser.c"
 	{
 	int _klen;
 	unsigned int _trans;
@@ -2862,103 +2868,103 @@ _match:
 		switch ( *_acts++ )
 		{
 	case 1:
-#line 2521 "upb/json/parser.rl"
+#line 2527 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 2:
-#line 2523 "upb/json/parser.rl"
+#line 2529 "upb/json/parser.rl"
 	{ p--; {stack[top++] = cs; cs = 23;goto _again;} }
 	break;
 	case 3:
-#line 2527 "upb/json/parser.rl"
+#line 2533 "upb/json/parser.rl"
 	{ start_text(parser, p); }
 	break;
 	case 4:
-#line 2528 "upb/json/parser.rl"
+#line 2534 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_text(parser, p)); }
 	break;
 	case 5:
-#line 2534 "upb/json/parser.rl"
+#line 2540 "upb/json/parser.rl"
 	{ start_hex(parser); }
 	break;
 	case 6:
-#line 2535 "upb/json/parser.rl"
+#line 2541 "upb/json/parser.rl"
 	{ hexdigit(parser, p); }
 	break;
 	case 7:
-#line 2536 "upb/json/parser.rl"
+#line 2542 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_hex(parser)); }
 	break;
 	case 8:
-#line 2542 "upb/json/parser.rl"
+#line 2548 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(escape(parser, p)); }
 	break;
 	case 9:
-#line 2548 "upb/json/parser.rl"
+#line 2554 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 10:
-#line 2560 "upb/json/parser.rl"
+#line 2566 "upb/json/parser.rl"
 	{ start_duration_base(parser, p); }
 	break;
 	case 11:
-#line 2561 "upb/json/parser.rl"
+#line 2567 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_duration_base(parser, p)); }
 	break;
 	case 12:
-#line 2563 "upb/json/parser.rl"
+#line 2569 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 13:
-#line 2568 "upb/json/parser.rl"
+#line 2574 "upb/json/parser.rl"
 	{ start_timestamp_base(parser, p); }
 	break;
 	case 14:
-#line 2569 "upb/json/parser.rl"
+#line 2575 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_timestamp_base(parser, p)); }
 	break;
 	case 15:
-#line 2571 "upb/json/parser.rl"
+#line 2577 "upb/json/parser.rl"
 	{ start_timestamp_fraction(parser, p); }
 	break;
 	case 16:
-#line 2572 "upb/json/parser.rl"
+#line 2578 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_timestamp_fraction(parser, p)); }
 	break;
 	case 17:
-#line 2574 "upb/json/parser.rl"
+#line 2580 "upb/json/parser.rl"
 	{ start_timestamp_zone(parser, p); }
 	break;
 	case 18:
-#line 2575 "upb/json/parser.rl"
+#line 2581 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_timestamp_zone(parser, p)); }
 	break;
 	case 19:
-#line 2577 "upb/json/parser.rl"
+#line 2583 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 20:
-#line 2582 "upb/json/parser.rl"
+#line 2588 "upb/json/parser.rl"
 	{ start_fieldmask_path_text(parser, p); }
 	break;
 	case 21:
-#line 2583 "upb/json/parser.rl"
+#line 2589 "upb/json/parser.rl"
 	{ end_fieldmask_path_text(parser, p); }
 	break;
 	case 22:
-#line 2588 "upb/json/parser.rl"
+#line 2594 "upb/json/parser.rl"
 	{ start_fieldmask_path(parser); }
 	break;
 	case 23:
-#line 2589 "upb/json/parser.rl"
+#line 2595 "upb/json/parser.rl"
 	{ end_fieldmask_path(parser); }
 	break;
 	case 24:
-#line 2595 "upb/json/parser.rl"
+#line 2601 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
 	case 25:
-#line 2600 "upb/json/parser.rl"
+#line 2606 "upb/json/parser.rl"
 	{
         if (is_wellknown_msg(parser, UPB_WELLKNOWN_TIMESTAMP)) {
           {stack[top++] = cs; cs = 47;goto _again;}
@@ -2972,11 +2978,11 @@ _match:
       }
 	break;
 	case 26:
-#line 2613 "upb/json/parser.rl"
+#line 2619 "upb/json/parser.rl"
 	{ p--; {stack[top++] = cs; cs = 78;goto _again;} }
 	break;
 	case 27:
-#line 2618 "upb/json/parser.rl"
+#line 2624 "upb/json/parser.rl"
 	{
         if (is_wellknown_msg(parser, UPB_WELLKNOWN_ANY)) {
           start_any_member(parser, p);
@@ -2986,11 +2992,11 @@ _match:
       }
 	break;
 	case 28:
-#line 2625 "upb/json/parser.rl"
+#line 2631 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_membername(parser)); }
 	break;
 	case 29:
-#line 2628 "upb/json/parser.rl"
+#line 2634 "upb/json/parser.rl"
 	{
         if (is_wellknown_msg(parser, UPB_WELLKNOWN_ANY)) {
           end_any_member(parser, p);
@@ -3000,7 +3006,7 @@ _match:
       }
 	break;
 	case 30:
-#line 2639 "upb/json/parser.rl"
+#line 2645 "upb/json/parser.rl"
 	{
         if (is_wellknown_msg(parser, UPB_WELLKNOWN_ANY)) {
           start_any_object(parser, p);
@@ -3010,7 +3016,7 @@ _match:
       }
 	break;
 	case 31:
-#line 2648 "upb/json/parser.rl"
+#line 2654 "upb/json/parser.rl"
 	{
         if (is_wellknown_msg(parser, UPB_WELLKNOWN_ANY)) {
           CHECK_RETURN_TOP(end_any_object(parser, p));
@@ -3020,54 +3026,54 @@ _match:
       }
 	break;
 	case 32:
-#line 2660 "upb/json/parser.rl"
+#line 2666 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_array(parser)); }
 	break;
 	case 33:
-#line 2664 "upb/json/parser.rl"
+#line 2670 "upb/json/parser.rl"
 	{ end_array(parser); }
 	break;
 	case 34:
-#line 2669 "upb/json/parser.rl"
+#line 2675 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_number(parser, p)); }
 	break;
 	case 35:
-#line 2670 "upb/json/parser.rl"
+#line 2676 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_number(parser, p)); }
 	break;
 	case 36:
-#line 2672 "upb/json/parser.rl"
+#line 2678 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_stringval(parser)); }
 	break;
 	case 37:
-#line 2673 "upb/json/parser.rl"
+#line 2679 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_stringval(parser)); }
 	break;
 	case 38:
-#line 2675 "upb/json/parser.rl"
+#line 2681 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, true)); }
 	break;
 	case 39:
-#line 2677 "upb/json/parser.rl"
+#line 2683 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, false)); }
 	break;
 	case 40:
-#line 2679 "upb/json/parser.rl"
+#line 2685 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_null(parser)); }
 	break;
 	case 41:
-#line 2681 "upb/json/parser.rl"
+#line 2687 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(start_subobject_full(parser)); }
 	break;
 	case 42:
-#line 2682 "upb/json/parser.rl"
+#line 2688 "upb/json/parser.rl"
 	{ end_subobject_full(parser); }
 	break;
 	case 43:
-#line 2687 "upb/json/parser.rl"
+#line 2693 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; goto _again;} }
 	break;
-#line 3071 "upb/json/parser.c"
+#line 3077 "upb/json/parser.c"
 		}
 	}
 
@@ -3084,32 +3090,32 @@ _again:
 	while ( __nacts-- > 0 ) {
 		switch ( *__acts++ ) {
 	case 0:
-#line 2519 "upb/json/parser.rl"
+#line 2525 "upb/json/parser.rl"
 	{ p--; {cs = stack[--top]; 	if ( p == pe )
 		goto _test_eof;
 goto _again;} }
 	break;
 	case 35:
-#line 2670 "upb/json/parser.rl"
+#line 2676 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_number(parser, p)); }
 	break;
 	case 38:
-#line 2675 "upb/json/parser.rl"
+#line 2681 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, true)); }
 	break;
 	case 39:
-#line 2677 "upb/json/parser.rl"
+#line 2683 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_bool(parser, false)); }
 	break;
 	case 40:
-#line 2679 "upb/json/parser.rl"
+#line 2685 "upb/json/parser.rl"
 	{ CHECK_RETURN_TOP(end_null(parser)); }
 	break;
 	case 42:
-#line 2682 "upb/json/parser.rl"
+#line 2688 "upb/json/parser.rl"
 	{ end_subobject_full(parser); }
 	break;
-#line 3113 "upb/json/parser.c"
+#line 3119 "upb/json/parser.c"
 		}
 	}
 	}
@@ -3117,7 +3123,7 @@ goto _again;} }
 	_out: {}
 	}
 
-#line 2715 "upb/json/parser.rl"
+#line 2721 "upb/json/parser.rl"
 
   if (p != pe) {
     upb_status_seterrf(parser->status, "Parse error at '%.*s'\n", pe - p, p);
@@ -3165,13 +3171,13 @@ static void json_parser_reset(upb_json_parser *p) {
 
   /* Emit Ragel initialization of the parser. */
   
-#line 3169 "upb/json/parser.c"
+#line 3175 "upb/json/parser.c"
 	{
 	cs = json_start;
 	top = 0;
 	}
 
-#line 2762 "upb/json/parser.rl"
+#line 2768 "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 1ae896af5b..75edb3b0bc 100644
--- a/upb/json/parser.rl
+++ b/upb/json/parser.rl
@@ -19,6 +19,9 @@
 ** - handling of keys/escape-sequences/etc that span input buffers.
 */
 
+/* Need to define _XOPEN_SOURCE before any include to make strptime work. */
+#define _XOPEN_SOURCE 700
+
 #include <ctype.h>
 #include <errno.h>
 #include <float.h>
@@ -28,10 +31,6 @@
 #include <stdlib.h>
 #include <string.h>
 
-/* Need to define __USE_XOPEN before including time.h to make strptime work. */
-#ifndef __USE_XOPEN
-#define __USE_XOPEN
-#endif
 #include <time.h>
 
 #include "upb/json/parser.h"
@@ -1535,11 +1534,18 @@ static bool end_timestamp_base(upb_json_parser *p, const char *ptr) {
   memcpy(timestamp_buf + UPB_TIMESTAMP_BASE_SIZE, "GMT", 3);
   timestamp_buf[UPB_TIMESTAMP_BASE_SIZE + 3] = 0;
 
+#if defined __MINGW32__ || defined __MINGW64__
+  upb_status_seterrf(
+      &p->status, "error parsing timestamp: mingw doesn't support strptime");
+  upb_env_reporterror(p->env, &p->status);
+  return false;
+#else
   /* Parse seconds */
   if (strptime(timestamp_buf, "%FT%H:%M:%S%Z", &p->tm) == NULL) {
     upb_status_seterrf(p->status, "error parsing timestamp: %s", buf);
     return false;
   }
+#endif
 
   /* Clean up buffer */
   multipart_end(p);