diff --git a/simgear/math/fastmath.cxx b/simgear/math/fastmath.cxx
index c95ccbcc..19968109 100644
--- a/simgear/math/fastmath.cxx
+++ b/simgear/math/fastmath.cxx
@@ -20,7 +20,7 @@
 
 
 
-#include <fastmath.hxx>
+#include "fastmath.hxx"
 
 /**
  * This function is on avarage 9 times faster than the system exp() function
diff --git a/simgear/math/fastmath.hxx b/simgear/math/fastmath.hxx
index 7ce8f461..6ebecd3f 100644
--- a/simgear/math/fastmath.hxx
+++ b/simgear/math/fastmath.hxx
@@ -25,7 +25,9 @@
 # error This library requires C++
 #endif
 
-
+#ifdef _MSC_VER
+#define  _USE_MATH_DEFINES
+#endif
 #include <math.h>