diff --git a/mrbgems/mruby-math/src/math.c b/mrbgems/mruby-math/src/math.c
index c182debea..c29ba6808 100644
--- a/mrbgems/mruby-math/src/math.c
+++ b/mrbgems/mruby-math/src/math.c
@@ -161,6 +161,10 @@ erfc(double x)
 
 #endif
 
+#if defined __FreeBSD__ && !defined __FreeBSD_version
+#include <osreldate.h> /* for __FreeBSD_version */
+#endif
+
 #if (defined _MSC_VER && _MSC_VER < 1800) || defined __ANDROID__ || (defined __FreeBSD__  &&  __FreeBSD_version < 803000)
 
 double