diff --git a/js/src/jit-test/tests/basic/testAssigningWatchedDeletedProperty.js b/js/src/jit-test/tests/basic/testAssigningWatchedDeletedProperty.js
new file mode 100644
index 000000000000..62fa710f5a98
--- /dev/null
+++ b/js/src/jit-test/tests/basic/testAssigningWatchedDeletedProperty.js
@@ -0,0 +1,7 @@
+var o = {};
+o.watch("p", function() { });
+
+for (var i = 0; i < HOTLOOP + 2; i++) {
+    o.p = 123;
+    delete o.p;
+}
diff --git a/js/src/jsdbgapi.cpp b/js/src/jsdbgapi.cpp
index de6b58526be3..f40244d144dd 100644
--- a/js/src/jsdbgapi.cpp
+++ b/js/src/jsdbgapi.cpp
@@ -576,9 +576,6 @@ struct JSWatchPoint {
 #define JSWP_LIVE       0x1             /* live because set and not cleared */
 #define JSWP_HELD       0x2             /* held while running handler/setter */
 
-static bool
-IsWatchedProperty(JSContext *cx, const Shape *shape);
-
 /*
  * NB: DropWatchPointAndUnlock releases cx->runtime->debuggerLock in all cases.
  */
@@ -770,7 +767,9 @@ js_watch_set_wrapper(JSContext *cx, uintN argc, Value *vp)
     return js_watch_set(cx, obj, userid, vp);
 }
 
-static bool
+namespace js {
+
+bool
 IsWatchedProperty(JSContext *cx, const Shape *shape)
 {
     if (shape->hasSetterValue()) {
@@ -778,12 +777,14 @@ IsWatchedProperty(JSContext *cx, const Shape *shape)
         if (!funobj || !funobj->isFunction())
             return false;
 
-        JSFunction *fun = GET_FUNCTION_PRIVATE(cx, funobj);
+        JSFunction *fun = funobj->getFunctionPrivate();
         return fun->maybeNative() == js_watch_set_wrapper;
     }
     return shape->setterOp() == js_watch_set;
 }
 
+}
+
 /*
  * Return an appropriate setter to substitute for |setter| on a property
  * with attributes |attrs|, to implement a watchpoint on the property named
diff --git a/js/src/jsdbgapi.h b/js/src/jsdbgapi.h
index fc476fac3f01..494d0eaf51d5 100644
--- a/js/src/jsdbgapi.h
+++ b/js/src/jsdbgapi.h
@@ -159,6 +159,13 @@ js_SweepWatchPoints(JSContext *cx);
 extern JSBool
 js_watch_set(JSContext *cx, JSObject *obj, jsid id, js::Value *vp);
 
+namespace js {
+
+bool
+IsWatchedProperty(JSContext *cx, const Shape *shape);
+
+}
+
 #endif
 
 #endif /* JS_HAS_OBJ_WATCHPOINT */
diff --git a/js/src/jstracer.cpp b/js/src/jstracer.cpp
index 08fc958596fb..6a40dbc465de 100644
--- a/js/src/jstracer.cpp
+++ b/js/src/jstracer.cpp
@@ -12241,6 +12241,11 @@ TraceRecorder::record_AddProperty(JSObject *obj)
     LIns* v_ins = get(&v);
     const Shape* shape = obj->lastProperty();
 
+    if (!shape->hasDefaultSetter()) {
+        JS_ASSERT(IsWatchedProperty(cx, shape));
+        RETURN_STOP_A("assignment adds property with watchpoint");
+    }
+
 #ifdef DEBUG
     JS_ASSERT(addPropShapeBefore);
     if (obj->inDictionaryMode())