diff --git a/php/ext/google/protobuf/php-upb.c b/php/ext/google/protobuf/php-upb.c
index 6f6952d32617..e59dd07b2358 100644
--- a/php/ext/google/protobuf/php-upb.c
+++ b/php/ext/google/protobuf/php-upb.c
@@ -6044,24 +6044,32 @@ upb_ExtensionRegistry* upb_ExtensionRegistry_New(upb_Arena* arena) {
   return r;
 }
 
-UPB_API bool upb_ExtensionRegistry_Add(upb_ExtensionRegistry* r,
-                                       const upb_MiniTableExtension* e) {
+UPB_API upb_ExtensionRegistryStatus upb_ExtensionRegistry_Add(
+    upb_ExtensionRegistry* r, const upb_MiniTableExtension* e) {
   char buf[EXTREG_KEY_SIZE];
   extreg_key(buf, e->UPB_PRIVATE(extendee), upb_MiniTableExtension_Number(e));
-  if (upb_strtable_lookup2(&r->exts, buf, EXTREG_KEY_SIZE, NULL)) return false;
-  return upb_strtable_insert(&r->exts, buf, EXTREG_KEY_SIZE,
-                             upb_value_constptr(e), r->arena);
+
+  if (upb_strtable_lookup2(&r->exts, buf, EXTREG_KEY_SIZE, NULL)) {
+    return kUpb_ExtensionRegistryStatus_DuplicateEntry;
+  }
+
+  if (!upb_strtable_insert(&r->exts, buf, EXTREG_KEY_SIZE,
+                           upb_value_constptr(e), r->arena)) {
+    return kUpb_ExtensionRegistryStatus_OutOfMemory;
+  }
+  return kUpb_ExtensionRegistryStatus_Ok;
 }
 
-bool upb_ExtensionRegistry_AddArray(upb_ExtensionRegistry* r,
-                                    const upb_MiniTableExtension** e,
-                                    size_t count) {
+upb_ExtensionRegistryStatus upb_ExtensionRegistry_AddArray(
+    upb_ExtensionRegistry* r, const upb_MiniTableExtension** e, size_t count) {
   const upb_MiniTableExtension** start = e;
   const upb_MiniTableExtension** end = UPB_PTRADD(e, count);
+  upb_ExtensionRegistryStatus status = kUpb_ExtensionRegistryStatus_Ok;
   for (; e < end; e++) {
-    if (!upb_ExtensionRegistry_Add(r, *e)) goto failure;
+    status = upb_ExtensionRegistry_Add(r, *e);
+    if (status != kUpb_ExtensionRegistryStatus_Ok) goto failure;
   }
-  return true;
+  return kUpb_ExtensionRegistryStatus_Ok;
 
 failure:
   // Back out the entries previously added.
@@ -6072,7 +6080,8 @@ bool upb_ExtensionRegistry_AddArray(upb_ExtensionRegistry* r,
                upb_MiniTableExtension_Number(ext));
     upb_strtable_remove2(&r->exts, buf, EXTREG_KEY_SIZE, NULL);
   }
-  return false;
+  UPB_ASSERT(status != kUpb_ExtensionRegistryStatus_Ok);
+  return status;
 }
 
 #ifdef UPB_LINKARR_DECLARE
@@ -6085,7 +6094,9 @@ bool upb_ExtensionRegistry_AddAllLinkedExtensions(upb_ExtensionRegistry* r) {
   for (const upb_MiniTableExtension* p = start; p < stop; p++) {
     // Windows can introduce zero padding, so we have to skip zeroes.
     if (upb_MiniTableExtension_Number(p) != 0) {
-      if (!upb_ExtensionRegistry_Add(r, p)) return false;
+      if (upb_ExtensionRegistry_Add(r, p) != kUpb_ExtensionRegistryStatus_Ok) {
+        return false;
+      }
     }
   }
   return true;
@@ -15425,9 +15436,16 @@ void _upb_FileDef_Create(upb_DefBuilder* ctx,
   }
 
   if (file->ext_count) {
-    bool ok = upb_ExtensionRegistry_AddArray(
+    upb_ExtensionRegistryStatus status = upb_ExtensionRegistry_AddArray(
         _upb_DefPool_ExtReg(ctx->symtab), file->ext_layouts, file->ext_count);
-    if (!ok) _upb_DefBuilder_OomErr(ctx);
+    if (status != kUpb_ExtensionRegistryStatus_Ok) {
+      if (status == kUpb_ExtensionRegistryStatus_OutOfMemory) {
+        _upb_DefBuilder_OomErr(ctx);
+      }
+
+      UPB_ASSERT(status == kUpb_ExtensionRegistryStatus_DuplicateEntry);
+      _upb_DefBuilder_Errf(ctx, "duplicate extension entry");
+    }
   }
 }
 
diff --git a/php/ext/google/protobuf/php-upb.h b/php/ext/google/protobuf/php-upb.h
index 14038f45ef5e..956177aee53f 100644
--- a/php/ext/google/protobuf/php-upb.h
+++ b/php/ext/google/protobuf/php-upb.h
@@ -5144,6 +5144,9 @@ upb_MiniTable* upb_MiniTable_BuildWithBuf(const char* data, size_t len,
 #ifndef UPB_MINI_TABLE_EXTENSION_REGISTRY_H_
 #define UPB_MINI_TABLE_EXTENSION_REGISTRY_H_
 
+#include <stddef.h>
+#include <stdint.h>
+
 
 // Must be last.
 
@@ -5187,21 +5190,25 @@ extern "C" {
 
 typedef struct upb_ExtensionRegistry upb_ExtensionRegistry;
 
+typedef enum {
+  kUpb_ExtensionRegistryStatus_Ok = 0,
+  kUpb_ExtensionRegistryStatus_DuplicateEntry = 1,
+  kUpb_ExtensionRegistryStatus_OutOfMemory = 2,
+} upb_ExtensionRegistryStatus;
+
 // Creates a upb_ExtensionRegistry in the given arena.
 // The arena must outlive any use of the extreg.
 UPB_API upb_ExtensionRegistry* upb_ExtensionRegistry_New(upb_Arena* arena);
 
-UPB_API bool upb_ExtensionRegistry_Add(upb_ExtensionRegistry* r,
-                                       const upb_MiniTableExtension* e);
+UPB_API upb_ExtensionRegistryStatus upb_ExtensionRegistry_Add(
+    upb_ExtensionRegistry* r, const upb_MiniTableExtension* e);
 
 // Adds the given extension info for the array |e| of size |count| into the
 // registry. If there are any errors, the entire array is backed out.
 // The extensions must outlive the registry.
 // Possible errors include OOM or an extension number that already exists.
-// TODO: There is currently no way to know the exact reason for failure.
-bool upb_ExtensionRegistry_AddArray(upb_ExtensionRegistry* r,
-                                    const upb_MiniTableExtension** e,
-                                    size_t count);
+upb_ExtensionRegistryStatus upb_ExtensionRegistry_AddArray(
+    upb_ExtensionRegistry* r, const upb_MiniTableExtension** e, size_t count);
 
 #ifdef UPB_LINKARR_DECLARE
 
diff --git a/ruby/ext/google/protobuf_c/ruby-upb.c b/ruby/ext/google/protobuf_c/ruby-upb.c
index c9a50024dc1b..7c2ceb9621bb 100644
--- a/ruby/ext/google/protobuf_c/ruby-upb.c
+++ b/ruby/ext/google/protobuf_c/ruby-upb.c
@@ -6044,24 +6044,32 @@ upb_ExtensionRegistry* upb_ExtensionRegistry_New(upb_Arena* arena) {
   return r;
 }
 
-UPB_API bool upb_ExtensionRegistry_Add(upb_ExtensionRegistry* r,
-                                       const upb_MiniTableExtension* e) {
+UPB_API upb_ExtensionRegistryStatus upb_ExtensionRegistry_Add(
+    upb_ExtensionRegistry* r, const upb_MiniTableExtension* e) {
   char buf[EXTREG_KEY_SIZE];
   extreg_key(buf, e->UPB_PRIVATE(extendee), upb_MiniTableExtension_Number(e));
-  if (upb_strtable_lookup2(&r->exts, buf, EXTREG_KEY_SIZE, NULL)) return false;
-  return upb_strtable_insert(&r->exts, buf, EXTREG_KEY_SIZE,
-                             upb_value_constptr(e), r->arena);
+
+  if (upb_strtable_lookup2(&r->exts, buf, EXTREG_KEY_SIZE, NULL)) {
+    return kUpb_ExtensionRegistryStatus_DuplicateEntry;
+  }
+
+  if (!upb_strtable_insert(&r->exts, buf, EXTREG_KEY_SIZE,
+                           upb_value_constptr(e), r->arena)) {
+    return kUpb_ExtensionRegistryStatus_OutOfMemory;
+  }
+  return kUpb_ExtensionRegistryStatus_Ok;
 }
 
-bool upb_ExtensionRegistry_AddArray(upb_ExtensionRegistry* r,
-                                    const upb_MiniTableExtension** e,
-                                    size_t count) {
+upb_ExtensionRegistryStatus upb_ExtensionRegistry_AddArray(
+    upb_ExtensionRegistry* r, const upb_MiniTableExtension** e, size_t count) {
   const upb_MiniTableExtension** start = e;
   const upb_MiniTableExtension** end = UPB_PTRADD(e, count);
+  upb_ExtensionRegistryStatus status = kUpb_ExtensionRegistryStatus_Ok;
   for (; e < end; e++) {
-    if (!upb_ExtensionRegistry_Add(r, *e)) goto failure;
+    status = upb_ExtensionRegistry_Add(r, *e);
+    if (status != kUpb_ExtensionRegistryStatus_Ok) goto failure;
   }
-  return true;
+  return kUpb_ExtensionRegistryStatus_Ok;
 
 failure:
   // Back out the entries previously added.
@@ -6072,7 +6080,8 @@ bool upb_ExtensionRegistry_AddArray(upb_ExtensionRegistry* r,
                upb_MiniTableExtension_Number(ext));
     upb_strtable_remove2(&r->exts, buf, EXTREG_KEY_SIZE, NULL);
   }
-  return false;
+  UPB_ASSERT(status != kUpb_ExtensionRegistryStatus_Ok);
+  return status;
 }
 
 #ifdef UPB_LINKARR_DECLARE
@@ -6085,7 +6094,9 @@ bool upb_ExtensionRegistry_AddAllLinkedExtensions(upb_ExtensionRegistry* r) {
   for (const upb_MiniTableExtension* p = start; p < stop; p++) {
     // Windows can introduce zero padding, so we have to skip zeroes.
     if (upb_MiniTableExtension_Number(p) != 0) {
-      if (!upb_ExtensionRegistry_Add(r, p)) return false;
+      if (upb_ExtensionRegistry_Add(r, p) != kUpb_ExtensionRegistryStatus_Ok) {
+        return false;
+      }
     }
   }
   return true;
@@ -14912,9 +14923,16 @@ void _upb_FileDef_Create(upb_DefBuilder* ctx,
   }
 
   if (file->ext_count) {
-    bool ok = upb_ExtensionRegistry_AddArray(
+    upb_ExtensionRegistryStatus status = upb_ExtensionRegistry_AddArray(
         _upb_DefPool_ExtReg(ctx->symtab), file->ext_layouts, file->ext_count);
-    if (!ok) _upb_DefBuilder_OomErr(ctx);
+    if (status != kUpb_ExtensionRegistryStatus_Ok) {
+      if (status == kUpb_ExtensionRegistryStatus_OutOfMemory) {
+        _upb_DefBuilder_OomErr(ctx);
+      }
+
+      UPB_ASSERT(status == kUpb_ExtensionRegistryStatus_DuplicateEntry);
+      _upb_DefBuilder_Errf(ctx, "duplicate extension entry");
+    }
   }
 }
 
diff --git a/ruby/ext/google/protobuf_c/ruby-upb.h b/ruby/ext/google/protobuf_c/ruby-upb.h
index 415fc6f63a9f..4854ecbe9221 100755
--- a/ruby/ext/google/protobuf_c/ruby-upb.h
+++ b/ruby/ext/google/protobuf_c/ruby-upb.h
@@ -5146,6 +5146,9 @@ upb_MiniTable* upb_MiniTable_BuildWithBuf(const char* data, size_t len,
 #ifndef UPB_MINI_TABLE_EXTENSION_REGISTRY_H_
 #define UPB_MINI_TABLE_EXTENSION_REGISTRY_H_
 
+#include <stddef.h>
+#include <stdint.h>
+
 
 // Must be last.
 
@@ -5189,21 +5192,25 @@ extern "C" {
 
 typedef struct upb_ExtensionRegistry upb_ExtensionRegistry;
 
+typedef enum {
+  kUpb_ExtensionRegistryStatus_Ok = 0,
+  kUpb_ExtensionRegistryStatus_DuplicateEntry = 1,
+  kUpb_ExtensionRegistryStatus_OutOfMemory = 2,
+} upb_ExtensionRegistryStatus;
+
 // Creates a upb_ExtensionRegistry in the given arena.
 // The arena must outlive any use of the extreg.
 UPB_API upb_ExtensionRegistry* upb_ExtensionRegistry_New(upb_Arena* arena);
 
-UPB_API bool upb_ExtensionRegistry_Add(upb_ExtensionRegistry* r,
-                                       const upb_MiniTableExtension* e);
+UPB_API upb_ExtensionRegistryStatus upb_ExtensionRegistry_Add(
+    upb_ExtensionRegistry* r, const upb_MiniTableExtension* e);
 
 // Adds the given extension info for the array |e| of size |count| into the
 // registry. If there are any errors, the entire array is backed out.
 // The extensions must outlive the registry.
 // Possible errors include OOM or an extension number that already exists.
-// TODO: There is currently no way to know the exact reason for failure.
-bool upb_ExtensionRegistry_AddArray(upb_ExtensionRegistry* r,
-                                    const upb_MiniTableExtension** e,
-                                    size_t count);
+upb_ExtensionRegistryStatus upb_ExtensionRegistry_AddArray(
+    upb_ExtensionRegistry* r, const upb_MiniTableExtension** e, size_t count);
 
 #ifdef UPB_LINKARR_DECLARE