1 files changed, 1 insertions, 0 deletions
diff --git a/complex.c b/complex.c
index beaf6713a1..e3c20139f2 100644
--- a/complex.c
+++ b/complex.c
@@ -5,6 +5,7 @@
   which is written in ruby.
 */
 
+#include "ruby/config.h"
 #if defined _MSC_VER
 /* Microsoft Visual C does not define M_PI and others by default */
 # define _USE_MATH_DEFINES 1