diff --git a/python/extension_dict.c b/python/extension_dict.c
index daf80e4a90..350b5f42cf 100644
--- a/python/extension_dict.c
+++ b/python/extension_dict.c
@@ -74,7 +74,7 @@ static PyObject* PyUpb_ExtensionDict_FindExtensionByNumber(PyObject* _self,
   const upb_ExtensionRegistry* reg = upb_DefPool_ExtensionRegistry(symtab);
   int64_t number = PyLong_AsLong(arg);
   const upb_MiniTable_Extension* ext =
-      (upb_MiniTable_Extension*)_upb_extreg_get(reg, l, number);
+      (upb_MiniTable_Extension*)upb_ExtensionRegistry_Lookup(reg, l, number);
   if (ext) {
     const upb_FieldDef* f = upb_DefPool_FindExtensionByMiniTable(symtab, ext);
     return PyUpb_FieldDescriptor_Get(f);
diff --git a/upb/decode.c b/upb/decode.c
index d5b9317380..f67579b29e 100644
--- a/upb/decode.c
+++ b/upb/decode.c
@@ -795,11 +795,11 @@ static void upb_Decoder_AddUnknownMessageSetItem(upb_Decoder* d,
 }
 
 static void upb_Decoder_AddMessageSetItem(upb_Decoder* d, upb_Message* msg,
-                                          const upb_MiniTable* layout,
+                                          const upb_MiniTable* t,
                                           uint32_t type_id, const char* data,
                                           uint32_t size) {
   const upb_MiniTable_Extension* item_mt =
-      _upb_extreg_get(d->extreg, layout, type_id);
+      upb_ExtensionRegistry_Lookup(d->extreg, t, type_id);
   if (item_mt) {
     upb_Decoder_AddKnownMessageSetItem(d, msg, item_mt, data, size);
   } else {
@@ -861,40 +861,40 @@ static const char* upb_Decoder_DecodeMessageSetItem(
 }
 
 static const upb_MiniTable_Field* _upb_Decoder_FindField(
-    upb_Decoder* d, const upb_MiniTable* l, uint32_t field_number,
+    upb_Decoder* d, const upb_MiniTable* t, uint32_t field_number,
     int* last_field_index) {
   static upb_MiniTable_Field none = {
       0, 0, 0, 0, kUpb_FakeFieldType_FieldNotFound, 0};
-  if (l == NULL) return &none;
+  if (t == NULL) return &none;
 
   size_t idx = ((size_t)field_number) - 1;  // 0 wraps to SIZE_MAX
-  if (idx < l->dense_below) {
+  if (idx < t->dense_below) {
     /* Fastest case: index into dense fields. */
     goto found;
   }
 
-  if (l->dense_below < l->field_count) {
+  if (t->dense_below < t->field_count) {
     /* Linear search non-dense fields. Resume scanning from last_field_index
      * since fields are usually in order. */
     int last = *last_field_index;
-    for (idx = last; idx < l->field_count; idx++) {
-      if (l->fields[idx].number == field_number) {
+    for (idx = last; idx < t->field_count; idx++) {
+      if (t->fields[idx].number == field_number) {
         goto found;
       }
     }
 
-    for (idx = l->dense_below; idx < last; idx++) {
-      if (l->fields[idx].number == field_number) {
+    for (idx = t->dense_below; idx < last; idx++) {
+      if (t->fields[idx].number == field_number) {
         goto found;
       }
     }
   }
 
   if (d->extreg) {
-    switch (l->ext) {
+    switch (t->ext) {
       case kUpb_ExtMode_Extendable: {
         const upb_MiniTable_Extension* ext =
-            _upb_extreg_get(d->extreg, l, field_number);
+            upb_ExtensionRegistry_Lookup(d->extreg, t, field_number);
         if (ext) return &ext->field;
         break;
       }
@@ -911,9 +911,9 @@ static const upb_MiniTable_Field* _upb_Decoder_FindField(
   return &none; /* Unknown field. */
 
 found:
-  UPB_ASSERT(l->fields[idx].number == field_number);
+  UPB_ASSERT(t->fields[idx].number == field_number);
   *last_field_index = idx;
-  return &l->fields[idx];
+  return &t->fields[idx];
 }
 
 int _upb_Decoder_GetVarintOp(const upb_MiniTable_Field* field) {
diff --git a/upb/extension_registry.c b/upb/extension_registry.c
index f811eddf8c..211652a678 100644
--- a/upb/extension_registry.c
+++ b/upb/extension_registry.c
@@ -54,8 +54,9 @@ upb_ExtensionRegistry* upb_ExtensionRegistry_New(upb_Arena* arena) {
   return r;
 }
 
-bool _upb_extreg_add(upb_ExtensionRegistry* r,
-                     const upb_MiniTable_Extension** e, size_t count) {
+bool upb_ExtensionRegistry_AddArray(upb_ExtensionRegistry* r,
+                                    const upb_MiniTable_Extension** e,
+                                    size_t count) {
   char buf[EXTREG_KEY_SIZE];
   const upb_MiniTable_Extension** start = e;
   const upb_MiniTable_Extension** end = UPB_PTRADD(e, count);
@@ -81,12 +82,11 @@ failure:
   return false;
 }
 
-const upb_MiniTable_Extension* _upb_extreg_get(const upb_ExtensionRegistry* r,
-                                               const upb_MiniTable* l,
-                                               uint32_t num) {
+const upb_MiniTable_Extension* upb_ExtensionRegistry_Lookup(
+    const upb_ExtensionRegistry* r, const upb_MiniTable* t, uint32_t num) {
   char buf[EXTREG_KEY_SIZE];
   upb_value v;
-  extreg_key(buf, l, num);
+  extreg_key(buf, t, num);
   if (upb_strtable_lookup2(&r->exts, buf, EXTREG_KEY_SIZE, &v)) {
     return upb_value_getconstptr(v);
   } else {
diff --git a/upb/extension_registry.h b/upb/extension_registry.h
index 10d6ad52cb..84eabca358 100644
--- a/upb/extension_registry.h
+++ b/upb/extension_registry.h
@@ -73,27 +73,23 @@ extern "C" {
  */
 
 typedef struct upb_ExtensionRegistry upb_ExtensionRegistry;
+typedef struct upb_MiniTable_Extension upb_MiniTable_Extension;
 
 // Creates a upb_ExtensionRegistry in the given arena.
 // The arena must outlive any use of the extreg.
 upb_ExtensionRegistry* upb_ExtensionRegistry_New(upb_Arena* arena);
 
-// EVERYTHING BELOW THIS LINE IS INTERNAL - DO NOT USE /////////////////////////
-
-typedef struct upb_MiniTable_Extension upb_MiniTable_Extension;
-
-// Adds the given extension info for message type |l| and field number |num|
-// into the registry. Returns false if this message type and field number were
-// already in the map, or if memory allocation fails.
-bool _upb_extreg_add(upb_ExtensionRegistry* r,
-                     const upb_MiniTable_Extension** e, size_t count);
+// 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.
+bool upb_ExtensionRegistry_AddArray(upb_ExtensionRegistry* r,
+                                    const upb_MiniTable_Extension** e,
+                                    size_t count);
 
-// Looks up the extension (if any) defined for message type |l| and field
-// number |num|. If an extension was found, copies the field info into |*ext|
-// and returns true. Otherwise returns false.
-const upb_MiniTable_Extension* _upb_extreg_get(const upb_ExtensionRegistry* r,
-                                               const upb_MiniTable* l,
-                                               uint32_t num);
+// Looks up the extension (if any) defined for message type |t| and field
+// number |num|. Returns the extension if found, otherwise NULL.
+const upb_MiniTable_Extension* upb_ExtensionRegistry_Lookup(
+    const upb_ExtensionRegistry* r, const upb_MiniTable* t, uint32_t num);
 
 #ifdef __cplusplus
 } /* extern "C" */
diff --git a/upb/fuzz_test_util.cc b/upb/fuzz_test_util.cc
index 219e4a3294..3ca4e89f31 100644
--- a/upb/fuzz_test_util.cc
+++ b/upb/fuzz_test_util.cc
@@ -144,9 +144,10 @@ void Builder::BuildExtensions(upb_ExtensionRegistry** exts) {
                                          status.ptr());
       if (!ptr) break;
       if (!LinkExtension(ext)) continue;
-      if (_upb_extreg_get(*exts, ext->extendee, ext->field.number)) continue;
-      _upb_extreg_add(*exts, const_cast<const upb_MiniTable_Extension**>(&ext),
-                      1);
+      if (upb_ExtensionRegistry_Lookup(*exts, ext->extendee, ext->field.number))
+        continue;
+      upb_ExtensionRegistry_AddArray(
+          *exts, const_cast<const upb_MiniTable_Extension**>(&ext), 1);
     }
   }
 }
diff --git a/upb/reflection/def_pool.c b/upb/reflection/def_pool.c
index 44679f3f8d..025cde8a80 100644
--- a/upb/reflection/def_pool.c
+++ b/upb/reflection/def_pool.c
@@ -411,8 +411,9 @@ const upb_FieldDef* upb_DefPool_FindExtensionByMiniTable(
 const upb_FieldDef* upb_DefPool_FindExtensionByNumber(const upb_DefPool* s,
                                                       const upb_MessageDef* m,
                                                       int32_t fieldnum) {
-  const upb_MiniTable* l = upb_MessageDef_MiniTable(m);
-  const upb_MiniTable_Extension* ext = _upb_extreg_get(s->extreg, l, fieldnum);
+  const upb_MiniTable* t = upb_MessageDef_MiniTable(m);
+  const upb_MiniTable_Extension* ext =
+      upb_ExtensionRegistry_Lookup(s->extreg, t, fieldnum);
   return ext ? upb_DefPool_FindExtensionByMiniTable(s, ext) : NULL;
 }
 
diff --git a/upb/reflection/file_def.c b/upb/reflection/file_def.c
index 0e6a8c1ab4..b0a8f63b33 100644
--- a/upb/reflection/file_def.c
+++ b/upb/reflection/file_def.c
@@ -338,8 +338,8 @@ void _upb_FileDef_Create(upb_DefBuilder* ctx,
   }
 
   if (file->ext_count) {
-    bool ok = _upb_extreg_add(_upb_DefPool_ExtReg(ctx->symtab),
-                              file->ext_layouts, file->ext_count);
+    bool ok = upb_ExtensionRegistry_AddArray(
+        _upb_DefPool_ExtReg(ctx->symtab), file->ext_layouts, file->ext_count);
     if (!ok) _upb_DefBuilder_OomErr(ctx);
   }
 }