diff --git a/src/libCom/osi/os/WIN32/epicsMath.h b/src/libCom/osi/os/WIN32/epicsMath.h
index d3778e664..b657b73d8 100644
--- a/src/libCom/osi/os/WIN32/epicsMath.h
+++ b/src/libCom/osi/os/WIN32/epicsMath.h
@@ -6,6 +6,6 @@
 #include <float.h>
 
 #define isnan(D) _isnan(D)
-#define isinf(D) (!_finite(D))
+#define isinf(D) ( !_finite(D) && !_isnan(D) ) 
 
 #endif /* epicsMathh */