--- a/hotspot/src/share/vm/oops/instanceKlass.cpp	Tue Mar 05 08:17:18 2013 -0800
+++ b/hotspot/src/share/vm/oops/instanceKlass.cpp	Tue Mar 05 18:03:36 2013 -0800
@@ -2170,7 +2170,11 @@
       if (impl != NULL) {
         if (!impl->is_loader_alive(is_alive)) {
           // remove this guy
-          *adr_implementor() = NULL;
+          Klass** klass = adr_implementor();
+          assert(klass != NULL, "null klass");
+          if (klass != NULL) {
+            *klass = NULL;
+          }
         }
       }
     }
@@ -3151,9 +3155,10 @@
   if (protection_domain() != NULL) {
     guarantee(protection_domain()->is_oop(), "should be oop");
   }
-  if (host_klass() != NULL) {
-    guarantee(host_klass()->is_metadata(), "should be in metaspace");
-    guarantee(host_klass()->is_klass(), "should be klass");
+  const Klass* host = host_klass();
+  if (host != NULL) {
+    guarantee(host->is_metadata(), "should be in metaspace");
+    guarantee(host->is_klass(), "should be klass");
   }
   if (signers() != NULL) {
     guarantee(signers()->is_objArray(), "should be obj array");

--- a/hotspot/src/share/vm/oops/instanceKlass.hpp	Tue Mar 05 08:17:18 2013 -0800
+++ b/hotspot/src/share/vm/oops/instanceKlass.hpp	Tue Mar 05 18:03:36 2013 -0800
@@ -536,7 +536,9 @@
     assert(is_anonymous(), "not anonymous");
     Klass** addr = (Klass**)adr_host_klass();
     assert(addr != NULL, "no reversed space");
-    *addr = host;
+    if (addr != NULL) {
+      *addr = host;
+    }
   }
   bool is_anonymous() const                {
     return (_misc_flags & _misc_is_anonymous) != 0;
@@ -758,7 +760,10 @@
   void set_implementor(Klass* k) {
     assert(is_interface(), "not interface");
     Klass** addr = adr_implementor();
-    *addr = k;
+    assert(addr != NULL, "null addr");
+    if (addr != NULL) {
+      *addr = k;
+    }
   }
 
   int  nof_implementors() const       {