diff --git a/php/ext/google/protobuf/php-upb.c b/php/ext/google/protobuf/php-upb.c
index 5527265f0c..e570089ed8 100644
--- a/php/ext/google/protobuf/php-upb.c
+++ b/php/ext/google/protobuf/php-upb.c
@@ -15126,7 +15126,10 @@ void _upb_MessageDef_InsertField(upb_DefBuilder* ctx, upb_MessageDef* m,
       _upb_MessageDef_Insert(m, shortname, shortnamelen, field_v, ctx->arena);
   if (!ok) _upb_DefBuilder_OomErr(ctx);
 
-  if (strcmp(shortname, json_name) != 0 &&
+  bool skip_json_conflicts =
+      UPB_DESC(MessageOptions_deprecated_legacy_json_field_conflicts)(
+          upb_MessageDef_Options(m));
+  if (!skip_json_conflicts && strcmp(shortname, json_name) != 0 &&
       UPB_DESC(FeatureSet_json_format)(m->resolved_features) ==
           UPB_DESC(FeatureSet_ALLOW) &&
       upb_strtable_lookup(&m->ntof, json_name, &v)) {
@@ -15136,14 +15139,16 @@ void _upb_MessageDef_InsertField(upb_DefBuilder* ctx, upb_MessageDef* m,
   }
 
   if (upb_strtable_lookup(&m->jtof, json_name, &v)) {
-    _upb_DefBuilder_Errf(ctx, "duplicate json_name (%s)", json_name);
+    if (!skip_json_conflicts) {
+      _upb_DefBuilder_Errf(ctx, "duplicate json_name (%s)", json_name);
+    }
+  } else {
+    const size_t json_size = strlen(json_name);
+    ok = upb_strtable_insert(&m->jtof, json_name, json_size,
+                             upb_value_constptr(f), ctx->arena);
+    if (!ok) _upb_DefBuilder_OomErr(ctx);
   }
 
-  const size_t json_size = strlen(json_name);
-  ok = upb_strtable_insert(&m->jtof, json_name, json_size,
-                           upb_value_constptr(f), ctx->arena);
-  if (!ok) _upb_DefBuilder_OomErr(ctx);
-
   if (upb_inttable_lookup(&m->itof, field_number, NULL)) {
     _upb_DefBuilder_Errf(ctx, "duplicate field number (%u)", field_number);
   }
diff --git a/ruby/ext/google/protobuf_c/ruby-upb.c b/ruby/ext/google/protobuf_c/ruby-upb.c
index bbbd7fc9bb..7eacee0490 100644
--- a/ruby/ext/google/protobuf_c/ruby-upb.c
+++ b/ruby/ext/google/protobuf_c/ruby-upb.c
@@ -14640,7 +14640,10 @@ void _upb_MessageDef_InsertField(upb_DefBuilder* ctx, upb_MessageDef* m,
       _upb_MessageDef_Insert(m, shortname, shortnamelen, field_v, ctx->arena);
   if (!ok) _upb_DefBuilder_OomErr(ctx);
 
-  if (strcmp(shortname, json_name) != 0 &&
+  bool skip_json_conflicts =
+      UPB_DESC(MessageOptions_deprecated_legacy_json_field_conflicts)(
+          upb_MessageDef_Options(m));
+  if (!skip_json_conflicts && strcmp(shortname, json_name) != 0 &&
       UPB_DESC(FeatureSet_json_format)(m->resolved_features) ==
           UPB_DESC(FeatureSet_ALLOW) &&
       upb_strtable_lookup(&m->ntof, json_name, &v)) {
@@ -14650,14 +14653,16 @@ void _upb_MessageDef_InsertField(upb_DefBuilder* ctx, upb_MessageDef* m,
   }
 
   if (upb_strtable_lookup(&m->jtof, json_name, &v)) {
-    _upb_DefBuilder_Errf(ctx, "duplicate json_name (%s)", json_name);
+    if (!skip_json_conflicts) {
+      _upb_DefBuilder_Errf(ctx, "duplicate json_name (%s)", json_name);
+    }
+  } else {
+    const size_t json_size = strlen(json_name);
+    ok = upb_strtable_insert(&m->jtof, json_name, json_size,
+                             upb_value_constptr(f), ctx->arena);
+    if (!ok) _upb_DefBuilder_OomErr(ctx);
   }
 
-  const size_t json_size = strlen(json_name);
-  ok = upb_strtable_insert(&m->jtof, json_name, json_size,
-                           upb_value_constptr(f), ctx->arena);
-  if (!ok) _upb_DefBuilder_OomErr(ctx);
-
   if (upb_inttable_lookup(&m->itof, field_number, NULL)) {
     _upb_DefBuilder_Errf(ctx, "duplicate field number (%u)", field_number);
   }