diff --git a/src/libCom/osi/os/WIN32/epicsMath.h b/src/libCom/osi/os/WIN32/epicsMath.h
index 8b9fc3a0f..d3778e664 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) _isinf(D)
+#define isinf(D) (!_finite(D))
 
 #endif /* epicsMathh */