diff --git a/sim/sh/interp.c b/sim/sh/interp.c
index 2bae4484e34..c4ac5b3e66b 100644
--- a/sim/sh/interp.c
+++ b/sim/sh/interp.c
@@ -65,8 +65,10 @@
 
 #ifdef _WIN32
 #include <float.h>		/* Needed for _isnan() */
+#ifndef isnan
 #define isnan _isnan
 #endif
+#endif
 
 #ifndef SIGBUS
 #define SIGBUS SIGSEGV