diff --git a/include/omnithread/atomic.h b/include/omnithread/atomic.h
index 3fed8df..e1b6a71 100644
--- a/include/omnithread/atomic.h
+++ b/include/omnithread/atomic.h
@@ -27,7 +27,7 @@
 #define __omnithread_atomic_h_
 
 
-#ifdef OMNI_HAVE_SYNC_ADD_AND_FETCH
+#if defined(OMNI_HAVE_SYNC_ADD_AND_FETCH) && !defined(_MSC_VER)
 
 #  define OMNI_REFCOUNT_DEFINED