diff --git a/js/src/jsapi.cpp b/js/src/jsapi.cpp
index d005723de3b..0c117cfe352 100644
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -1323,20 +1323,13 @@ JS_LeaveCrossCompartmentCall(JSCrossCompartmentCall *call)
 bool
 JSAutoEnterCompartment::enter(JSContext *cx, JSObject *target)
 {
-    JS_ASSERT(state == STATE_UNENTERED);
-    if (cx->compartment == target->getCompartment()) {
-        state = STATE_SAME_COMPARTMENT;
+    JS_ASSERT(!call);
+    if (cx->compartment == target->compartment()) {
+        call = reinterpret_cast<JSCrossCompartmentCall*>(1);
         return true;
     }
-
-    JS_STATIC_ASSERT(sizeof(bytes) == sizeof(AutoCompartment));
-    CHECK_REQUEST(cx);
-    AutoCompartment *call = new (bytes) AutoCompartment(cx, target);
-    if (call->enter()) {
-        state = STATE_OTHER_COMPARTMENT;
-        return true;
-    }
-    return false;
+    call = JS_EnterCrossCompartmentCall(cx, target);
+    return call != NULL;
 }
 
 void
@@ -1345,15 +1338,6 @@ JSAutoEnterCompartment::enterAndIgnoreErrors(JSContext *cx, JSObject *target)
     (void) enter(cx, target);
 }
 
-JSAutoEnterCompartment::~JSAutoEnterCompartment()
-{
-    if (state == STATE_OTHER_COMPARTMENT) {
-        AutoCompartment* ac = reinterpret_cast<AutoCompartment*>(bytes);
-        CHECK_REQUEST(ac->context);
-        ac->~AutoCompartment();
-    }
-}
-
 namespace JS {
 
 bool
diff --git a/js/src/jsapi.h b/js/src/jsapi.h
index 28ca2a3b4fd..63530844d52 100644
--- a/js/src/jsapi.h
+++ b/js/src/jsapi.h
@@ -2214,41 +2214,27 @@ JS_END_EXTERN_C
 
 class JS_PUBLIC_API(JSAutoEnterCompartment)
 {
-    /*
-     * This is a poor man's Maybe<AutoCompartment>, because we don't have
-     * access to the AutoCompartment definition here.  We statically assert in
-     * jsapi.cpp that we have the right size here.
-     */
-#ifndef _MSC_VER
-    void* bytes[13];
-#else
-    void* bytes[sizeof(void*) == 4 ? 16 : 13];
-#endif
-
-    /*
-     * This object may be in one of three states.  If enter() or
-     * enterAndIgnoreErrors() hasn't been called, it's in STATE_UNENTERED.
-     * Otherwise, if we were asked to enter into the current compartment, our
-     * state is STATE_SAME_COMPARTMENT.  If we actually created an
-     * AutoCompartment and entered another compartment, our state is
-     * STATE_OTHER_COMPARTMENT.
-     */
-    enum State {
-        STATE_UNENTERED,
-        STATE_SAME_COMPARTMENT,
-        STATE_OTHER_COMPARTMENT
-    } state;
+    JSCrossCompartmentCall *call;
 
   public:
-    JSAutoEnterCompartment() : state(STATE_UNENTERED) {}
+    JSAutoEnterCompartment() : call(NULL) {}
 
     bool enter(JSContext *cx, JSObject *target);
 
     void enterAndIgnoreErrors(JSContext *cx, JSObject *target);
 
-    bool entered() const { return state != STATE_UNENTERED; }
+    bool entered() const { return call != NULL; }
 
-    ~JSAutoEnterCompartment();
+    ~JSAutoEnterCompartment() {
+        if (call && call != reinterpret_cast<JSCrossCompartmentCall*>(1))
+            JS_LeaveCrossCompartmentCall(call);
+    }
+
+    void swap(JSAutoEnterCompartment &other) {
+        JSCrossCompartmentCall *tmp = call;
+        call = other.call;
+        other.call = tmp;
+    }
 };
 
 JS_BEGIN_EXTERN_C