Index: src/OFObject.m
==================================================================
--- src/OFObject.m
+++ src/OFObject.m
@@ -217,11 +217,11 @@
 	OFObject *instance;
 	size_t instanceSize;
 
 	instanceSize = class_getInstanceSize(class);
 
-	if OF_UNLIKELY (extraAlignment > 0)
+	if OF_UNLIKELY (extraAlignment > 1)
 		extraAlignment = ((instanceSize + extraAlignment - 1) &
 		    ~(extraAlignment - 1)) - extraAlignment;
 
 	instance = malloc(PRE_IVARS_ALIGN + instanceSize +
 	    extraAlignment + extraSize);

Index: src/runtime/class.m
==================================================================
--- src/runtime/class.m
+++ src/runtime/class.m
@@ -198,10 +198,40 @@
 
 	cls->superclass->subclass_list[i] = cls;
 	cls->superclass->subclass_list[i + 1] = Nil;
 }
 
+
+static void
+update_ivar_offsets(Class cls)
+{
+	unsigned i;
+
+	if (!(cls->info & OBJC_CLASS_INFO_NEW_ABI))
+		return;
+
+	if (cls->instance_size > 0)
+		return;
+
+	cls->instance_size = -cls->instance_size;
+
+	if (cls->superclass != Nil) {
+		cls->instance_size += cls->superclass->instance_size;
+
+		if (cls->ivars != NULL) {
+			for (i = 0; i < cls->ivars->count; i++) {
+				cls->ivars->ivars[i].offset +=
+				    cls->superclass->instance_size;
+				*cls->ivar_offsets[i] =
+				    cls->ivars->ivars[i].offset;
+			}
+		}
+	} else
+		for (i = 0; i < cls->ivars->count; i++)
+			*cls->ivar_offsets[i] = cls->ivars->ivars[i].offset;
+}
+
 static void
 setup_class(Class cls)
 {
 	const char *superclass;
 
@@ -224,10 +254,12 @@
 
 		add_subclass(cls);
 		add_subclass(cls->isa);
 	} else
 		cls->isa->superclass = cls;
+
+	update_ivar_offsets(cls);
 
 	cls->info |= OBJC_CLASS_INFO_SETUP;
 	cls->isa->info |= OBJC_CLASS_INFO_SETUP;
 }
 

Index: src/runtime/runtime-private.h
==================================================================
--- src/runtime/runtime-private.h
+++ src/runtime/runtime-private.h
@@ -20,20 +20,20 @@
 	struct objc_abi_class *metaclass;
 	const char *superclass;
 	const char *name;
 	unsigned long version;
 	unsigned long info;
-	unsigned long instance_size;
+	long instance_size;
 	void *ivars;
 	struct objc_abi_method_list *methodlist;
 	void *dtable;
 	void *subclass_list;
 	void *sibling_class;
 	void *protocols;
 	void *gc_object_type;
 	long abi_version;
-	void *ivar_offsets;
+	int32_t **ivar_offsets;
 	void *properties;
 };
 
 struct objc_abi_method {
 	const char *name;

Index: src/runtime/runtime.h
==================================================================
--- src/runtime/runtime.h
+++ src/runtime/runtime.h
@@ -39,20 +39,20 @@
 	Class isa;
 	Class superclass;
 	const char *name;
 	unsigned long version;
 	unsigned long info;
-	unsigned long instance_size;
+	long instance_size;
 	struct objc_ivar_list *ivars;
 	struct objc_method_list *methodlist;
 	struct objc_sparsearray *dtable;
 	Class *subclass_list;
 	void *sibling_class;
 	struct objc_protocol_list *protocols;
 	void *gc_object_type;
 	unsigned long abi_version;
-	void *ivar_offsets;
+	int32_t **ivar_offsets;
 	struct objc_property_list *properties;
 };
 
 enum objc_class_info {
 	OBJC_CLASS_INFO_CLASS	    = 0x001,