diff --git a/simgear/scene/sky/cloud.cxx b/simgear/scene/sky/cloud.cxx
index 606dd52a..e5b475ae 100644
--- a/simgear/scene/sky/cloud.cxx
+++ b/simgear/scene/sky/cloud.cxx
@@ -24,10 +24,13 @@
 // #if defined (__APPLE__) 
 // // any C++ header file undefines isinf and isnan
 // // so this should be included before <iostream>
-// inline int (isinf)(double r) { return isinf(r); }
 // inline int (isnan)(double r) { return isnan(r); } 
 // #endif
 
+#if defined(__MINGW32__)
+#define isnan(x) _isnan(x)
+#endif
+
 // #include STL_IOSTREAM
 
 #include <plib/sg.h>