diff --git a/arc.m b/arc.m
index 1a4f7773..687651b1 100644
--- a/arc.m
+++ b/arc.m
@@ -45,7 +45,7 @@ static inline DWORD arc_tls_key_create(void WINAPI(*cleanupFunction)(void*))
 
 extern void _NSConcreteMallocBlock;
 extern void _NSConcreteStackBlock;
-extern void _NSConcreteGlobalBlock;
+extern struct objc_class _NSConcreteGlobalBlock;
 
 @interface NSAutoreleasePool
 + (Class)class;
@@ -190,6 +190,12 @@ static inline id retain(id obj)
 {
 	if (isSmallObject(obj)) { return obj; }
 	Class cls = obj->isa;
+
+	if ((Class)&_NSConcreteGlobalBlock == cls->isa)
+	{
+		cls = cls->isa;
+	}
+
 	if ((Class)&_NSConcreteMallocBlock == cls ||
 	    (Class)&_NSConcreteStackBlock == cls)
 	{
@@ -214,13 +220,14 @@ static inline void release(id obj)
 {
 	if (isSmallObject(obj)) { return; }
 	Class cls = obj->isa;
+
 	if (cls == &_NSConcreteMallocBlock)
 	{
 		_Block_release(obj);
 		return;
 	}
 	if ((cls == &_NSConcreteStackBlock) ||
-	    (cls == &_NSConcreteGlobalBlock))
+	    (cls->isa == &_NSConcreteGlobalBlock))
 	{
 		return;
 	}
diff --git a/class.h b/class.h
index 8da94eb2..e41afac4 100644
--- a/class.h
+++ b/class.h
@@ -300,6 +300,10 @@ static inline Class classForObject(id obj)
 			return SmallObjectClasses[(addr & OBJC_SMALL_OBJECT_MASK)];
 		}
 	}
+	extern struct objc_class _NSConcreteGlobalBlock;
+	if (obj->isa->isa == (Class)&_NSConcreteGlobalBlock) {
+		return (Class)&_NSConcreteGlobalBlock;
+	}
 	return obj->isa;
 }