diff --git a/src/messages.cc b/src/messages.cc
index 9489071403..5f89860b2f 100644
--- a/src/messages.cc
+++ b/src/messages.cc
@@ -144,10 +144,13 @@ base::SmartArrayPointer<char> MessageHandler::GetLocalizedMessage(
 
 CallSite::CallSite(Isolate* isolate, Handle<JSObject> call_site_obj)
     : isolate_(isolate) {
+  Handle<Object> maybe_function = JSObject::GetDataProperty(
+      call_site_obj, isolate->factory()->call_site_function_symbol());
+  if (!maybe_function->IsJSFunction()) return;
+
+  fun_ = Handle<JSFunction>::cast(maybe_function);
   receiver_ = JSObject::GetDataProperty(
       call_site_obj, isolate->factory()->call_site_receiver_symbol());
-  fun_ = Handle<JSFunction>::cast(JSObject::GetDataProperty(
-      call_site_obj, isolate->factory()->call_site_function_symbol()));
   pos_ = Handle<Smi>::cast(JSObject::GetDataProperty(
                                call_site_obj,
                                isolate->factory()->call_site_position_symbol()))
diff --git a/src/messages.h b/src/messages.h
index 0282c6fb7d..a47bf57d45 100644
--- a/src/messages.h
+++ b/src/messages.h
@@ -62,6 +62,8 @@ class CallSite {
   bool IsEval();
   bool IsConstructor();
 
+  bool IsValid() { return !fun_.is_null(); }
+
  private:
   Isolate* isolate_;
   Handle<Object> receiver_;
diff --git a/src/runtime/runtime-internal.cc b/src/runtime/runtime-internal.cc
index 90d5532af3..fdf3961a5f 100644
--- a/src/runtime/runtime-internal.cc
+++ b/src/runtime/runtime-internal.cc
@@ -318,6 +318,7 @@ RUNTIME_FUNCTION(Runtime_FormatMessageString) {
     CONVERT_ARG_HANDLE_CHECKED(JSObject, call_site_obj, 0); \
     Handle<String> result;                                  \
     CallSite call_site(isolate, call_site_obj);             \
+    RUNTIME_ASSERT(call_site.IsValid())                     \
     return RETURN(call_site.NAME(), isolate);               \
   }
 
diff --git a/test/mjsunit/regress-crbug-528379.js b/test/mjsunit/regress-crbug-528379.js
new file mode 100644
index 0000000000..f335f6a104
--- /dev/null
+++ b/test/mjsunit/regress-crbug-528379.js
@@ -0,0 +1,8 @@
+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --enable-slow-asserts
+
+Error.prepareStackTrace = function(e, frames) { return frames; }
+assertThrows(function() { new Error().stack[0].getMethodName.call({}); });