diff --git a/dlls/ntdll/Makefile.in b/dlls/ntdll/Makefile.in
index f39ffb42c6f..341123f7488 100644
--- a/dlls/ntdll/Makefile.in
+++ b/dlls/ntdll/Makefile.in
@@ -44,6 +44,7 @@ C_SRCS = \
 	threadpool.c \
 	time.c \
 	unix/cdrom.c \
+	unix/cmpxchg64.c \
 	unix/debug.c \
 	unix/env.c \
 	unix/file.c \
diff --git a/dlls/ntdll/unix/cmpxchg64.c b/dlls/ntdll/unix/cmpxchg64.c
new file mode 100644
index 00000000000..032e32bb4c2
--- /dev/null
+++ b/dlls/ntdll/unix/cmpxchg64.c
@@ -0,0 +1,64 @@
+/*
+ * Large integer functions
+ *
+ * Copyright 2000 Alexandre Julliard
+ * Copyright 2003 Thomas Mertes
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
+ */
+
+#if 0
+#pragma makedep unix
+#endif
+
+#include <stdarg.h>
+
+#include "ntstatus.h"
+#define WIN32_NO_STATUS
+#include "windef.h"
+#include "winternl.h"
+#include "wine/asm.h"
+
+
+#ifndef _WIN64
+
+/*************************************************************************
+ *        RtlInterlockedCompareExchange64   (NTDLL.@)
+ */
+#ifndef __GCC_HAVE_SYNC_COMPARE_AND_SWAP_8
+__ASM_STDCALL_FUNC(RtlInterlockedCompareExchange64, 20,
+                   "push %ebx\n\t"
+                   __ASM_CFI(".cfi_adjust_cfa_offset 4\n\t")
+                   __ASM_CFI(".cfi_rel_offset %ebx,0\n\t")
+                   "push %esi\n\t"
+                   __ASM_CFI(".cfi_adjust_cfa_offset 4\n\t")
+                   __ASM_CFI(".cfi_rel_offset %esi,0\n\t")
+                   "movl 12(%esp),%esi\n\t"
+                   "movl 16(%esp),%ebx\n\t"
+                   "movl 20(%esp),%ecx\n\t"
+                   "movl 24(%esp),%eax\n\t"
+                   "movl 28(%esp),%edx\n\t"
+                   "lock; cmpxchg8b (%esi)\n\t"
+                   "pop %esi\n\t"
+                   __ASM_CFI(".cfi_same_value %esi\n\t")
+                   __ASM_CFI(".cfi_adjust_cfa_offset -4\n\t")
+                   "pop %ebx\n\t"
+                   __ASM_CFI(".cfi_same_value %ebx\n\t")
+                   __ASM_CFI(".cfi_adjust_cfa_offset -4\n\t")
+                   "ret $20")
+#endif
+
+#endif  /* _WIN64 */
+