Index: src/OFBlock.m
==================================================================
--- src/OFBlock.m
+++ src/OFBlock.m
@@ -70,34 +70,34 @@
 @end
 
 #ifdef OF_OBJFW_RUNTIME
 /* Begin of ObjC module */
 static struct objc_class _NSConcreteStackBlock_metaclass = {
-	(Class)(void *)"OFObject", (Class)(void *)"OFBlock", "OFStackBlock", 8,
-	OBJC_CLASS_INFO_METACLASS, sizeof(struct objc_class), NULL, NULL
+	Nil, Nil, "OFStackBlock", 8, OBJC_CLASS_INFO_METACLASS,
+	sizeof(_NSConcreteStackBlock_metaclass), NULL, NULL
 };
 
 struct objc_class _NSConcreteStackBlock = {
 	&_NSConcreteStackBlock_metaclass, (Class)(void *)"OFBlock",
 	"OFStackBlock", 8, OBJC_CLASS_INFO_CLASS, sizeof(of_block_literal_t),
 	NULL, NULL
 };
 
 static struct objc_class _NSConcreteGlobalBlock_metaclass = {
-	(Class)(void *)"OFObject", (Class)(void *)"OFBlock", "OFGlobalBlock", 8,
-	OBJC_CLASS_INFO_METACLASS, sizeof(struct objc_class), NULL, NULL
+	Nil, Nil, "OFGlobalBlock", 8, OBJC_CLASS_INFO_METACLASS,
+	sizeof(_NSConcreteGlobalBlock_metaclass), NULL, NULL
 };
 
 struct objc_class _NSConcreteGlobalBlock = {
 	&_NSConcreteGlobalBlock_metaclass, (Class)(void *)"OFBlock",
 	"OFGlobalBlock", 8, OBJC_CLASS_INFO_CLASS, sizeof(of_block_literal_t),
 	NULL, NULL
 };
 
 static struct objc_class _NSConcreteMallocBlock_metaclass = {
-	(Class)(void *)"OFObject", (Class)(void *)"OFBlock", "OFMallocBlock", 8,
-	OBJC_CLASS_INFO_METACLASS, sizeof(struct objc_class), NULL, NULL
+	Nil, Nil, "OFMallocBlock", 8, OBJC_CLASS_INFO_METACLASS,
+	sizeof(_NSConcreteMallocBlock_metaclass), NULL, NULL
 };
 
 struct objc_class _NSConcreteMallocBlock = {
 	&_NSConcreteMallocBlock_metaclass, (Class)(void *)"OFBlock",
 	"OFMallocBlock", 8, OBJC_CLASS_INFO_CLASS, sizeof(of_block_literal_t),

Index: src/runtime/class.m
==================================================================
--- src/runtime/class.m
+++ src/runtime/class.m
@@ -292,26 +292,38 @@
 		return;
 
 	superclassName = (const char *)class->superclass;
 	if (superclassName != NULL) {
 		Class super = objc_classname_to_class(superclassName, false);
+		Class rootClass;
 
 		if (super == Nil)
 			return;
 
 		setupClass(super);
 
 		if (!(super->info & OBJC_CLASS_INFO_SETUP))
 			return;
 
+		/*
+		 * GCC sets class->isa->isa to the name of the root class,
+		 * while Clang just sets it to Nil. Therefore always calculate
+		 * it.
+		 */
+		for (Class iter = super; iter != NULL; iter = iter->superclass)
+			rootClass = iter;
+
 		class->superclass = super;
+		class->isa->isa = rootClass->isa;
 		class->isa->superclass = super->isa;
 
 		addSubclass(class);
 		addSubclass(class->isa);
-	} else
+	} else {
+		class->isa->isa = class->isa;
 		class->isa->superclass = class;
+	}
 
 	updateIvarOffsets(class);
 
 	class->info |= OBJC_CLASS_INFO_SETUP;
 	class->isa->info |= OBJC_CLASS_INFO_SETUP;