Index: src/OFObject.m
==================================================================
--- src/OFObject.m
+++ src/OFObject.m
@@ -334,12 +334,13 @@
 	size_t instanceSize;
 
 	instanceSize = class_getInstanceSize(class);
 
 	if OF_UNLIKELY (extraAlignment > 1)
-		extraAlignment = ((instanceSize + extraAlignment - 1) &
-		    ~(extraAlignment - 1)) - extraAlignment;
+		extraAlignment = OFRoundUpToPowerOf2(extraAlignment,
+		    PRE_IVARS_ALIGN + instanceSize) -
+		    PRE_IVARS_ALIGN - instanceSize;
 
 	instance = calloc(1, PRE_IVARS_ALIGN + instanceSize +
 	    extraAlignment + extraSize);
 
 	if OF_UNLIKELY (instance == nil) {