diff --git a/js/src/jsprobes.cpp b/js/src/jsprobes.cpp
index c786e8e98e2..5a59e556718 100644
--- a/js/src/jsprobes.cpp
+++ b/js/src/jsprobes.cpp
@@ -217,33 +217,33 @@ Probes::JITWatcher::CollectNativeRegions(RegionVector &regions,
 }
 
 void
-Probes::registerMJITCode(JSContext *cx, js::mjit::JITScript *jscr,
+Probes::registerMJITCode(JSContext *cx, js::mjit::JITChunk *chunk,
                          js::mjit::JSActiveFrame *outerFrame,
                          js::mjit::JSActiveFrame **inlineFrames,
                          void *mainCodeAddress, size_t mainCodeSize,
                          void *stubCodeAddress, size_t stubCodeSize)
 {
     for (JITWatcher **p = jitWatchers.begin(); p != jitWatchers.end(); ++p)
-        (*p)->registerMJITCode(cx, jscr, outerFrame,
+        (*p)->registerMJITCode(cx, chunk, outerFrame,
                                inlineFrames,
                                mainCodeAddress, mainCodeSize,
                                stubCodeAddress, stubCodeSize);
 }
 
 void
-Probes::discardMJITCode(FreeOp *fop, mjit::JITScript *jscr, JSScript *script, void* address)
+Probes::discardMJITCode(FreeOp *fop, mjit::JITScript *jscr, mjit::JITChunk *chunk, void* address)
 {
     for (JITWatcher **p = jitWatchers.begin(); p != jitWatchers.end(); ++p)
-        (*p)->discardMJITCode(fop, jscr, script, address);
+        (*p)->discardMJITCode(fop, jscr, chunk, address);
 }
 
 void
 Probes::registerICCode(JSContext *cx,
-                       mjit::JITScript *jscr, JSScript *script, jsbytecode* pc,
+                       mjit::JITChunk *chunk, JSScript *script, jsbytecode* pc,
                        void *start, size_t size)
 {
     for (JITWatcher **p = jitWatchers.begin(); p != jitWatchers.end(); ++p)
-        (*p)->registerICCode(cx, jscr, script, pc, start, size);
+        (*p)->registerICCode(cx, chunk, script, pc, start, size);
 }
 #endif
 
diff --git a/js/src/jsprobes.h b/js/src/jsprobes.h
index 1c44f96c7ee..c64daf4e211 100644
--- a/js/src/jsprobes.h
+++ b/js/src/jsprobes.h
@@ -258,17 +258,17 @@ public:
                                      mjit::JSActiveFrame *outerFrame,
                                      mjit::JSActiveFrame **inlineFrames);
 
-    virtual void registerMJITCode(JSContext *cx, js::mjit::JITScript *jscr,
+    virtual void registerMJITCode(JSContext *cx, js::mjit::JITChunk *chunk,
                                   mjit::JSActiveFrame *outerFrame,
                                   mjit::JSActiveFrame **inlineFrames,
                                   void *mainCodeAddress, size_t mainCodeSize,
                                   void *stubCodeAddress, size_t stubCodeSize) = 0;
 
-    virtual void discardMJITCode(FreeOp *fop, mjit::JITScript *jscr, JSScript *script,
+    virtual void discardMJITCode(FreeOp *fop, mjit::JITScript *jscr, mjit::JITChunk *chunk,
                                  void* address) = 0;
 
     virtual void registerICCode(JSContext *cx,
-                                js::mjit::JITScript *jscr, JSScript *script, jsbytecode* pc,
+                                js::mjit::JITChunk *chunk, JSScript *script, jsbytecode* pc,
                                 void *start, size_t size) = 0;
 #endif
 
@@ -306,7 +306,7 @@ JITGranularityRequested();
  * New method JIT code has been created
  */
 void
-registerMJITCode(JSContext *cx, js::mjit::JITScript *jscr,
+registerMJITCode(JSContext *cx, js::mjit::JITChunk *chunk,
                  mjit::JSActiveFrame *outerFrame,
                  mjit::JSActiveFrame **inlineFrames,
                  void *mainCodeAddress, size_t mainCodeSize,
@@ -316,14 +316,14 @@ registerMJITCode(JSContext *cx, js::mjit::JITScript *jscr,
  * Method JIT code is about to be discarded
  */
 void
-discardMJITCode(FreeOp *fop, mjit::JITScript *jscr, JSScript *script, void* address);
+discardMJITCode(FreeOp *fop, mjit::JITScript *jscr, mjit::JITChunk *chunk, void* address);
 
 /*
- * IC code has been allocated within the given JITScript
+ * IC code has been allocated within the given JITChunk
  */
 void
 registerICCode(JSContext *cx,
-               mjit::JITScript *jscr, JSScript *script, jsbytecode* pc,
+               mjit::JITChunk *chunk, JSScript *script, jsbytecode* pc,
                void *start, size_t size);
 #endif /* JS_METHODJIT */
 
diff --git a/js/src/methodjit/BaseCompiler.h b/js/src/methodjit/BaseCompiler.h
index 24f65022da4..ad31e63fdf4 100644
--- a/js/src/methodjit/BaseCompiler.h
+++ b/js/src/methodjit/BaseCompiler.h
@@ -171,7 +171,7 @@ class LinkerHelper : public JSC::LinkBuffer
     JSC::CodeLocationLabel finalize(VMFrame &f) {
         masm.finalize(*this);
         JSC::CodeLocationLabel label = finalizeCodeAddendum();
-        Probes::registerICCode(f.cx, f.jit(), f.script(), f.pc(),
+        Probes::registerICCode(f.cx, f.chunk(), f.script(), f.pc(),
                                label.executableAddress(), masm.size());
         return label;
     }
diff --git a/js/src/methodjit/Compiler.cpp b/js/src/methodjit/Compiler.cpp
index f9d47fdd84c..aeed084fbb7 100644
--- a/js/src/methodjit/Compiler.cpp
+++ b/js/src/methodjit/Compiler.cpp
@@ -1774,7 +1774,7 @@ mjit::Compiler::finishThisUp()
     JSC::ExecutableAllocator::makeExecutable(result, masm.size() + stubcc.size());
     JSC::ExecutableAllocator::cacheFlush(result, masm.size() + stubcc.size());
 
-    Probes::registerMJITCode(cx, jit,
+    Probes::registerMJITCode(cx, chunk,
                              a,
                              (JSActiveFrame**) inlineFrames.begin(),
                              result, masm.size(),
diff --git a/js/src/methodjit/MethodJIT.cpp b/js/src/methodjit/MethodJIT.cpp
index 66162ad9d2d..49ea633e221 100644
--- a/js/src/methodjit/MethodJIT.cpp
+++ b/js/src/methodjit/MethodJIT.cpp
@@ -1328,7 +1328,7 @@ JITScript::destroyChunk(FreeOp *fop, unsigned chunkIndex, bool resetUses)
     ChunkDescriptor &desc = chunkDescriptor(chunkIndex);
 
     if (desc.chunk) {
-        Probes::discardMJITCode(fop, this, script, desc.chunk->code.m_code.executableAddress());
+        Probes::discardMJITCode(fop, this, desc.chunk, desc.chunk->code.m_code.executableAddress());
         fop->delete_(desc.chunk);
         desc.chunk = NULL;
 
@@ -1484,6 +1484,8 @@ JITScript::nativeToPC(void *returnAddress, CallSite **pinline)
     JITChunk *chunk = findCodeChunk(returnAddress);
     JS_ASSERT(chunk);
 
+    JS_ASSERT(chunk->isValidCode(returnAddress));
+
     size_t low = 0;
     size_t high = chunk->nCallICs;
     js::mjit::ic::CallICInfo *callICs_ = chunk->callICs();