Index: configure.ac
==================================================================
--- configure.ac
+++ configure.ac
@@ -215,10 +215,20 @@
 				AC_SUBST(LOOKUP_S, lookup-x86-elf.S)
 				AC_DEFINE(OF_ASM_LOOKUP, 1,
 					[Whether to use lookup in assembly])
 			])
 		])
+
+		AC_EGREP_CPP(yes, [
+			#if defined(__amd64__) && defined(__MACH__)
+			yes
+			#endif
+		], [
+			AC_SUBST(LOOKUP_S, lookup-amd64-macho.S)
+			AC_DEFINE(OF_ASM_LOOKUP, 1,
+				[Whether to use lookup in assembly])
+		])
 
 		AS_IF([test x"$enable_seluid16" = x"yes"], [
 			AC_DEFINE(OF_SELUID16, 1,
 				[Whether to use 16 bit selector UIDs])
 		])

ADDED   src/runtime/lookup-amd64-macho.S
Index: src/runtime/lookup-amd64-macho.S
==================================================================
--- /dev/null
+++ src/runtime/lookup-amd64-macho.S
@@ -0,0 +1,66 @@
+/*
+ * Copyright (c) 2008, 2009, 2010, 2011, 2012
+ *   Jonathan Schleifer <js@webkeks.org>
+ *
+ * All rights reserved.
+ *
+ * This file is part of ObjFW. It may be distributed under the terms of the
+ * Q Public License 1.0, which can be found in the file LICENSE.QPL included in
+ * the packaging of this file.
+ *
+ * Alternatively, it may be distributed under the terms of the GNU General
+ * Public License, either version 2 or 3, which can be found in the file
+ * LICENSE.GPLv2 or LICENSE.GPLv3 respectively included in the packaging of this
+ * file.
+ */
+
+#include "config.h"
+
+.globl _objc_msg_lookup
+.globl _objc_msg_lookup_super
+
+.section __TEXT, __text, regular, pure_instructions
+_objc_msg_lookup:
+	testq	%rdi, %rdi
+	jz	ret_nil
+
+	movq	(%rdi), %r8
+	movq	64(%r8), %r8
+
+lookup:
+	movq	(%rsi), %rax
+	movzbl	%ah, %ecx
+	movzbl	%al, %edx
+#ifndef OF_SELUID16
+	shrl	$16, %eax
+
+	movq	(%r8,%rax,8), %r8
+#endif
+	movq	(%r8,%rcx,8), %r8
+	movq	(%r8,%rdx,8), %rax
+
+	testq	%rax, %rax
+	jz	forward
+
+	ret
+
+forward:
+	jmp	_objc_not_found_handler
+
+_objc_msg_lookup_super:
+	movq	(%rdi), %rax
+	testq	%rax, %rax
+	jz	ret_nil
+
+	movq	8(%rdi), %r8
+	movq	64(%r8), %r8
+	movq	%rdi, %rax
+	jmp	lookup
+
+ret_nil:
+	leaq	nil_method(%rip), %rax
+	ret
+
+nil_method:
+	movq	%rdi, %rax
+	ret