diff --git a/src/gravity.c b/src/gravity.c
index 4f8fdc12b..3af3e7ac9 100644
--- a/src/gravity.c
+++ b/src/gravity.c
@@ -1,4 +1,5 @@
 #include <math.h>
+#include <sys/types.h>
 #include <pthread.h>
 #include "defines.h"
 #include "gravity.h"