diff --git a/src/objects/js-objects.cc b/src/objects/js-objects.cc
index 803072e8b7..902e350b45 100644
--- a/src/objects/js-objects.cc
+++ b/src/objects/js-objects.cc
@@ -3690,12 +3690,12 @@ Maybe<PropertyAttributes> JSObject::GetPropertyAttributesWithInterceptor(
 void JSObject::NormalizeProperties(Isolate* isolate, Handle<JSObject> object,
                                    PropertyNormalizationMode mode,
                                    int expected_additional_properties,
-                                   const char* reason) {
+                                   bool use_cache, const char* reason) {
   if (!object->HasFastProperties()) return;
 
   Handle<Map> map(object->map(), isolate);
-  Handle<Map> new_map =
-      Map::Normalize(isolate, map, map->elements_kind(), mode, reason);
+  Handle<Map> new_map = Map::Normalize(isolate, map, map->elements_kind(), mode,
+                                       use_cache, reason);
 
   JSObject::MigrateToMap(isolate, object, new_map,
                          expected_additional_properties);
@@ -4756,20 +4756,41 @@ void JSObject::OptimizeAsPrototype(Handle<JSObject> object,
                                    bool enable_setup_mode) {
   Isolate* isolate = object->GetIsolate();
   if (object->IsJSGlobalObject()) return;
-  if (enable_setup_mode && PrototypeBenefitsFromNormalization(object)) {
-    // First normalize to ensure all JSFunctions are DATA_CONSTANT.
-    JSObject::NormalizeProperties(isolate, object, KEEP_INOBJECT_PROPERTIES, 0,
-                                  "NormalizeAsPrototype");
-  }
-  if (object->map().is_prototype_map()) {
+  if (object->map(isolate).is_prototype_map()) {
+    if (enable_setup_mode && PrototypeBenefitsFromNormalization(object)) {
+      // This is the only way PrototypeBenefitsFromNormalization can be true:
+      DCHECK(!object->map(isolate).should_be_fast_prototype_map());
+      // First normalize to ensure all JSFunctions are DATA_CONSTANT.
+      constexpr bool kUseCache = true;
+      JSObject::NormalizeProperties(isolate, object, KEEP_INOBJECT_PROPERTIES,
+                                    0, kUseCache, "NormalizeAsPrototype");
+    }
     if (!V8_DICT_PROPERTY_CONST_TRACKING_BOOL &&
-        object->map().should_be_fast_prototype_map() &&
+        object->map(isolate).should_be_fast_prototype_map() &&
         !object->HasFastProperties()) {
       JSObject::MigrateSlowToFast(object, 0, "OptimizeAsPrototype");
     }
   } else {
-    Handle<Map> new_map =
-        Map::Copy(isolate, handle(object->map(), isolate), "CopyAsPrototype");
+    Handle<Map> new_map;
+    if (enable_setup_mode && PrototypeBenefitsFromNormalization(object)) {
+#if DEBUG
+      Handle<Map> old_map = handle(object->map(isolate), isolate);
+#endif  // DEBUG
+      // First normalize to ensure all JSFunctions are DATA_CONSTANT. Don't use
+      // the cache, since we're going to use the normalized version directly,
+      // without making a copy.
+      constexpr bool kUseCache = false;
+      JSObject::NormalizeProperties(isolate, object, KEEP_INOBJECT_PROPERTIES,
+                                    0, kUseCache,
+                                    "NormalizeAndCopyAsPrototype");
+      // A new map was created.
+      DCHECK_NE(*old_map, object->map(isolate));
+
+      new_map = handle(object->map(isolate), isolate);
+    } else {
+      new_map =
+          Map::Copy(isolate, handle(object->map(), isolate), "CopyAsPrototype");
+    }
     new_map->set_is_prototype_map(true);
 
     // Replace the pointer to the exact constructor with the Object function
@@ -4810,8 +4831,9 @@ void JSObject::OptimizeAsPrototype(Handle<JSObject> object,
 #ifdef DEBUG
   bool should_be_dictionary = V8_DICT_PROPERTY_CONST_TRACKING_BOOL &&
                               enable_setup_mode && !object->IsJSGlobalProxy() &&
-                              !object->GetIsolate()->bootstrapper()->IsActive();
-  DCHECK_IMPLIES(should_be_dictionary, object->map().is_dictionary_map());
+                              !isolate->bootstrapper()->IsActive();
+  DCHECK_IMPLIES(should_be_dictionary,
+                 object->map(isolate).is_dictionary_map());
 #endif
 }
 
diff --git a/src/objects/js-objects.h b/src/objects/js-objects.h
index 002c9d0500..608e84acbf 100644
--- a/src/objects/js-objects.h
+++ b/src/objects/js-objects.h
@@ -651,7 +651,15 @@ class JSObject : public TorqueGeneratedJSObject<JSObject, JSReceiver> {
   // an initial capacity for holding these properties.
   V8_EXPORT_PRIVATE static void NormalizeProperties(
       Isolate* isolate, Handle<JSObject> object, PropertyNormalizationMode mode,
-      int expected_additional_properties, const char* reason);
+      int expected_additional_properties, bool use_cache, const char* reason);
+
+  V8_EXPORT_PRIVATE static void NormalizeProperties(
+      Isolate* isolate, Handle<JSObject> object, PropertyNormalizationMode mode,
+      int expected_additional_properties, const char* reason) {
+    const bool kUseCache = true;
+    NormalizeProperties(isolate, object, mode, expected_additional_properties,
+                        kUseCache, reason);
+  }
 
   // Convert and update the elements backing store to be a
   // NumberDictionary dictionary.  Returns the backing after conversion.
diff --git a/src/objects/map-inl.h b/src/objects/map-inl.h
index 7355e70533..7105676b31 100644
--- a/src/objects/map-inl.h
+++ b/src/objects/map-inl.h
@@ -171,7 +171,9 @@ void Map::GeneralizeIfCanHaveTransitionableFastElementsKind(
 
 Handle<Map> Map::Normalize(Isolate* isolate, Handle<Map> fast_map,
                            PropertyNormalizationMode mode, const char* reason) {
-  return Normalize(isolate, fast_map, fast_map->elements_kind(), mode, reason);
+  const bool kUseCache = true;
+  return Normalize(isolate, fast_map, fast_map->elements_kind(), mode,
+                   kUseCache, reason);
 }
 
 bool Map::EquivalentToForNormalization(const Map other,
diff --git a/src/objects/map.cc b/src/objects/map.cc
index 0db0b71104..f487f02ac8 100644
--- a/src/objects/map.cc
+++ b/src/objects/map.cc
@@ -1182,13 +1182,15 @@ Handle<Map> Map::RawCopy(Isolate* isolate, Handle<Map> src_handle,
 
 Handle<Map> Map::Normalize(Isolate* isolate, Handle<Map> fast_map,
                            ElementsKind new_elements_kind,
-                           PropertyNormalizationMode mode, const char* reason) {
+                           PropertyNormalizationMode mode, bool use_cache,
+                           const char* reason) {
   DCHECK(!fast_map->is_dictionary_map());
 
   Handle<Object> maybe_cache(isolate->native_context()->normalized_map_cache(),
                              isolate);
-  bool use_cache =
-      !fast_map->is_prototype_map() && !maybe_cache->IsUndefined(isolate);
+  if (fast_map->is_prototype_map() || maybe_cache->IsUndefined(isolate)) {
+    use_cache = false;
+  }
   Handle<NormalizedMapCache> cache;
   if (use_cache) cache = Handle<NormalizedMapCache>::cast(maybe_cache);
 
diff --git a/src/objects/map.h b/src/objects/map.h
index 0fe14ffcec..5f934a1237 100644
--- a/src/objects/map.h
+++ b/src/objects/map.h
@@ -534,11 +534,17 @@ class Map : public TorqueGeneratedMap<Map, HeapObject> {
       Isolate* isolate, Handle<Map> old_map, InternalIndex descriptor_number,
       PropertyConstness constness, Handle<Object> value);
 
+  V8_EXPORT_PRIVATE static Handle<Map> Normalize(
+      Isolate* isolate, Handle<Map> map, ElementsKind new_elements_kind,
+      PropertyNormalizationMode mode, bool use_cache, const char* reason);
   V8_EXPORT_PRIVATE static Handle<Map> Normalize(Isolate* isolate,
                                                  Handle<Map> map,
                                                  ElementsKind new_elements_kind,
                                                  PropertyNormalizationMode mode,
-                                                 const char* reason);
+                                                 const char* reason) {
+    const bool kUseCache = true;
+    return Normalize(isolate, map, new_elements_kind, mode, kUseCache, reason);
+  }
 
   inline static Handle<Map> Normalize(Isolate* isolate, Handle<Map> fast_map,
                                       PropertyNormalizationMode mode,