diff --git a/Test/AllocatePair.m b/Test/AllocatePair.m
index cab64a7..3afeb48 100644
--- a/Test/AllocatePair.m
+++ b/Test/AllocatePair.m
@@ -15,6 +15,8 @@ int main()
 {
 	Class a, b, c, d, e;
 
+	assert(class_getInstanceSize(objc_allocateClassPair(Nil, "Empty", 0)) == sizeof(Class));
+	a = objc_allocateClassPair([Test class], "A", 0);
 	a = objc_allocateClassPair([Test class], "A", 0);
 	objc_registerClassPair(a);
 
diff --git a/runtime.c b/runtime.c
index 4352ccc..14a8d9e 100644
--- a/runtime.c
+++ b/runtime.c
@@ -726,7 +726,7 @@ Class objc_allocateClassPair(Class superclass, const char *name, size_t extraByt
 
 	if (Nil == superclass)
 	{
-		newClass->instance_size = sizeof(struct objc_class);
+		newClass->instance_size = sizeof(struct objc_class*);
 	}
 	else
 	{