Index: src/OFObject.h
==================================================================
--- src/OFObject.h
+++ src/OFObject.h
@@ -396,12 +396,15 @@
 
 /**
  * \brief Adds all instance methods from the specified class to the class that
  *	  is the receiver.
  *
- * Existing methods will not be overriden, so that it behaves similar to normal
- * inheritance.
+ * Methods implemented by the receiving class itself will not be overridden,
+ * however methods implemented by its superclass will. Therefore it behaves
+ * similar as if the specified class is the superclass of the receiver.
+ *
+ * The specified class may not use instance variables and has to use accessors.
  *
  * \param class The class from which the instance methods should be inherited
  */
 + (void)inheritInstanceMethodsFromClass: (Class)class;
 

Index: src/OFObject.m
==================================================================
--- src/OFObject.m
+++ src/OFObject.m
@@ -26,10 +26,11 @@
 
 #include <assert.h>
 
 #import "OFObject.h"
 #import "OFArray.h"
+#import "OFSet.h"
 #import "OFIntrospection.h"
 #import "OFAutoreleasePool.h"
 
 #import "OFAllocFailedException.h"
 #import "OFEnumerationMutationException.h"
@@ -463,28 +464,43 @@
 }
 
 + (void)inheritInstanceMethodsFromClass: (Class)class
 {
 	OFAutoreleasePool *pool = [[OFAutoreleasePool alloc] init];
+	OFMutableSet *set = [OFMutableSet set];
 	OFIntrospection *introspection;
 	OFMethod **cArray;
 	size_t i, count;
+
+	introspection = [OFIntrospection introspectionWithClass: self];
+	cArray = [[introspection instanceMethods] cArray];
+	count = [[introspection instanceMethods] count];
+
+	for (i = 0; i < count; i++)
+		[set addObject: [cArray[i] name]];
 
 	introspection = [OFIntrospection introspectionWithClass: class];
 	cArray = [[introspection instanceMethods] cArray];
 	count = [[introspection instanceMethods] count];
 
 	for (i = 0; i < count; i++) {
 		SEL selector;
 		IMP implementation;
+
+		if ([set containsObject: [cArray[i] name]])
+			continue;
 
 		selector = [cArray[i] selector];
 		implementation = [class instanceMethodForSelector: selector];
 
-		[self addInstanceMethod: selector
-		       withTypeEncoding: [cArray[i] typeEncoding]
-			 implementation: implementation];
+		if ([self respondsToSelector: selector])
+			[self setImplementation: implementation
+			      forInstanceMethod: selector];
+		else
+			[self addInstanceMethod: selector
+			       withTypeEncoding: [cArray[i] typeEncoding]
+				 implementation: implementation];
 	}
 
 	[pool release];
 }