Index: src/OFXMLElement.m
==================================================================
--- src/OFXMLElement.m
+++ src/OFXMLElement.m
@@ -239,11 +239,12 @@
 			[all_namespaces setObject: obj
 					   forKey: key];
 	} else
 		all_namespaces = namespaces;
 
-	prefix = [all_namespaces objectForKey: (ns != nil ? ns : @"")];
+	prefix = [all_namespaces objectForKey:
+	    (ns != nil ? ns : (OFString*)@"")];
 
 	i = 0;
 	len = [name cStringLength] + 3;
 	str_c = [self allocMemoryWithSize: len];