diff --git a/indra/llcommon/llfasttimer.h b/indra/llcommon/llfasttimer.h
index 7e3c411758d6ce85b89c43ee4781823498f72e6d..5058a2e772d33cc67b86c03c2b1668041132df73 100644
--- a/indra/llcommon/llfasttimer.h
+++ b/indra/llcommon/llfasttimer.h
@@ -39,9 +39,13 @@
 #define TIME_FAST_TIMERS 0
 
 #if LL_WINDOWS
-#define _interlockedbittestandset _dummy_func
+// because MS has different signatures for these functions in winnt.h
+// need to rename them to avoid conflicts
+#define _interlockedbittestandset _renamed_interlockedbittestandset
+#define _interlockedbittestandreset _renamed_interlockedbittestandreset
 #include <intrin.h>
 #undef _interlockedbittestandset
+#undef _interlockedbittestandreset
 
 #define LL_INLINE __forceinline
 // shift off lower 8 bits for lower resolution but longer term timing