1 files changed, 2 insertions, 0 deletions

diff --git a/geo.c b/geo.c
index 84c73cf..6178bf6 100644
--- a/geo.c
+++ b/geo.c
@@ -1,3 +1,5 @@
+#include <stddef.h>
+
 #include "balls.h"
 
 int