--- old/src/share/vm/code/nmethod.cpp	2013-08-21 09:41:17.632701606 +0200
+++ new/src/share/vm/code/nmethod.cpp	2013-08-21 09:41:17.462044697 +0200
@@ -93,18 +93,21 @@
 #endif
 
 bool nmethod::is_compiled_by_c1() const {
-  if (compiler() == NULL || method() == NULL)  return false;  // can happen during debug printing
-  if (is_native_method()) return false;
+  if (compiler() == NULL)  return false;
+  // method() == NULL can happen during debug printing or if the nmethod is zombie
+  assert(method() == NULL || !is_native_method(), "native methods have no compiler");
   return compiler()->is_c1();
 }
 bool nmethod::is_compiled_by_c2() const {
-  if (compiler() == NULL || method() == NULL)  return false;  // can happen during debug printing
-  if (is_native_method()) return false;
+  if (compiler() == NULL)  return false;
+  // method() == NULL can happen during debug printing or if the nmethod is zombie
+  assert(method() == NULL || !is_native_method(), "native methods have no compiler");
   return compiler()->is_c2();
 }
 bool nmethod::is_compiled_by_shark() const {
-  if (is_native_method()) return false;
-  assert(compiler() != NULL, "must be");
+  if (compiler() == NULL)  return false;
+  // method() == NULL can happen during debug printing or if the nmethod is zombie
+  assert(method() == NULL || !is_native_method(), "native methods have no compiler");
   return compiler()->is_shark();
 }
 
@@ -1382,6 +1385,8 @@
     // nmethods aren't scanned for GC.
     _oops_are_stale = true;
 #endif
+    _method = NULL; // the Method may be reclaimed by class unloading
+                    // now that the nmethod is in zombie state
   } else {
     assert(state == not_entrant, "other cases may need to be handled differently");
   }