diff --git a/src/dlmalloc_2_8_6.c b/src/dlmalloc_2_8_6.c
index d117229..4a5c241 100644
--- a/src/dlmalloc_2_8_6.c
+++ b/src/dlmalloc_2_8_6.c
@@ -1853,8 +1853,8 @@ static FORCEINLINE void x86_clear_lock(int* sl) {
 #define CLEAR_LOCK(sl)   x86_clear_lock(sl)
 
 #else /* Win32 MSC */
-#define CAS_LOCK(sl)     interlockedexchange(sl, (LONG)1)
-#define CLEAR_LOCK(sl)   interlockedexchange (sl, (LONG)0)
+#define CAS_LOCK(sl)     interlockedexchange((volatile long*)sl, (LONG)1)
+#define CLEAR_LOCK(sl)   interlockedexchange ((volatile long*)sl, (LONG)0)
 
 #endif /* ... gcc spins locks ... */