diff --git a/src/include/os/WIN32/epicsMath.h b/src/include/os/WIN32/epicsMath.h
index 236a640c0..8eb33e41a 100644
--- a/src/include/os/WIN32/epicsMath.h
+++ b/src/include/os/WIN32/epicsMath.h
@@ -5,6 +5,6 @@
 #include <float.h>
 
 #define isnan(D) _isnan(D)
-#define isinf(D) _isinf(D)
+#define isinf(D) ( !_finite(D) && !_isnan(D) ) 
 
 #endif /* epicsMathh */