--- old/src/hotspot/share/classfile/moduleEntry.cpp	2018-05-24 13:18:16.086401116 -0400
+++ new/src/hotspot/share/classfile/moduleEntry.cpp	2018-05-24 13:18:14.136451505 -0400
@@ -25,7 +25,7 @@
 #include "precompiled.hpp"
 #include "jni.h"
 #include "classfile/classLoaderData.inline.hpp"
-#include "classfile/javaClasses.hpp"
+#include "classfile/javaClasses.inline.hpp"
 #include "classfile/moduleEntry.hpp"
 #include "logging/log.hpp"
 #include "memory/resourceArea.hpp"
@@ -236,10 +236,14 @@
   // The java.lang.Module for this loader's
   // corresponding unnamed module can be found in the java.lang.ClassLoader object.
   oop module = java_lang_ClassLoader::unnamedModule(cld->class_loader());
+
+  // Ensure that the unnamed module was correctly set when
+  // the class loader was constructed.
+  guarantee(java_lang_Module::is_instance(module), "unnamed module is not an instance of type java.lang.Module");
+
   ModuleEntry* unnamed_module = new_unnamed_module_entry(Handle(Thread::current(), module), cld);
 
-  // Store pointer to the ModuleEntry in the unnamed module's java.lang.Module
-  // object.
+  // Store pointer to the ModuleEntry in the unnamed module's java.lang.Module object.
   java_lang_Module::set_module_entry(module, unnamed_module);
 
   return unnamed_module;