Index: src/OFObject.h
==================================================================
--- src/OFObject.h
+++ src/OFObject.h
@@ -477,10 +477,30 @@
  *
  * \param class The class from which the instance methods should be inherited
  */
 + (void)inheritMethodsFromClass: (Class)class_;
 
+/**
+ * \brief Try to resolve the specified class method.
+ *
+ * This method is called if a class method was not found, so that an
+ * implementation can be provided at runtime.
+ *
+ * \return Whether the method has been added to the class
+ */
++ (BOOL)resolveClassMethod: (SEL)selector;
+
+/**
+ * \brief Try to resolve the specified instance method.
+ *
+ * This method is called if an instance method was not found, so that an
+ * implementation can be provided at runtime.
+ *
+ * \return Whether the method has been added to the class
+ */
++ (BOOL)resolveInstanceMethod: (SEL)selector;
+
 /**
  * \brief Initializes an already allocated object.
  *
  * Derived classes may override this, but need to do self = [super init] before
  * they do any initialization themselves. init may never return nil, instead

Index: src/OFObject.m
==================================================================
--- src/OFObject.m
+++ src/OFObject.m
@@ -101,11 +101,11 @@
 
 #if !defined(OF_APPLE_RUNTIME) || defined(__OBJC2__)
 static void
 uncaught_exception_handler(id exception)
 {
-	fprintf(stderr, "\nUnhandled exception:\n%s\n",
+	fprintf(stderr, "\nRuntime error: Unhandled exception:\n%s\n",
 	    [[exception description] UTF8String]);
 }
 #endif
 
 static void
@@ -113,10 +113,60 @@
 {
 	@throw [OFEnumerationMutationException
 	    exceptionWithClass: [object class]
 			object: object];
 }
+
+#ifdef OF_OBJFW_RUNTIME
+static id
+method_not_found_handler(id obj, SEL sel, ...)
+{
+	fprintf(stderr, "Runtime error: Selector %s is not implemented in "
+	    "class %s!\n", sel_getName(sel),
+	    class_getName(object_getClass(obj)));
+	abort();
+}
+
+static IMP
+forward_handler(id obj, SEL sel)
+{
+	if (class_isMetaClass(object_getClass(obj))) {
+		if (![obj respondsToSelector: @selector(resolveClassMethod:)])
+			return method_not_found_handler;
+
+		if (![obj resolveClassMethod: sel])
+			return method_not_found_handler;
+
+		if (![obj respondsToSelector: sel]) {
+			fprintf(stderr, "Runtime error: [%s "
+			    "resolveClassMethod: %s] returned YES without "
+			    "adding the method!\n", class_getName(obj),
+			    sel_getName(sel));
+			abort();
+		}
+	} else {
+		Class c = object_getClass(obj);
+
+		if (![c respondsToSelector: @selector(resolveInstanceMethod:)])
+			return method_not_found_handler;
+
+		if (![c resolveInstanceMethod: sel])
+			return method_not_found_handler;
+
+		if (![obj respondsToSelector: sel]) {
+			fprintf(stderr, "Runtime error: [%s "
+			    "resolveInstanceMethod: %s] returned YES without "
+			    "adding the method!\n",
+			    class_getName(object_getClass(obj)),
+			    sel_getName(sel));
+			abort();
+		}
+	}
+
+	return objc_msg_lookup(obj, sel);
+}
+#endif
 
 #ifndef HAVE_OBJC_ENUMERATIONMUTATION
 void
 objc_enumerationMutation(id object)
 {
@@ -200,10 +250,14 @@
 #endif
 
 #if !defined(OF_APPLE_RUNTIME) || defined(__OBJC2__)
 	objc_setUncaughtExceptionHandler(uncaught_exception_handler);
 #endif
+
+#ifdef OF_OBJFW_RUNTIME
+	objc_forward_handler = forward_handler;
+#endif
 
 #ifdef HAVE_OBJC_ENUMERATIONMUTATION
 	objc_setEnumerationMutationHandler(enumeration_mutation_handler);
 #endif
 
@@ -461,10 +515,20 @@
 	}
 #endif
 
 	[self inheritMethodsFromClass: [class superclass]];
 }
+
++ (BOOL)resolveClassMethod: (SEL)selector
+{
+	return NO;
+}
+
++ (BOOL)resolveInstanceMethod: (SEL)selector
+{
+	return NO;
+}
 
 - init
 {
 	Class class;
 	void (*last)(id, SEL) = NULL;