diff --git a/simgear/constants.h b/simgear/constants.h
index b77a7965..e3bd3c1e 100644
--- a/simgear/constants.h
+++ b/simgear/constants.h
@@ -32,6 +32,9 @@
 
 #include <simgear/compiler.h>
 
+#ifdef _MSC_VER
+#  define  _USE_MATH_DEFINES
+#endif
 #ifdef SG_HAVE_STD_INCLUDES
 #  include <cmath>
 #else