diff --git a/lib/hilbert.h b/lib/hilbert.h
index b4ea07e..2caa42e 100644
--- a/lib/hilbert.h
+++ b/lib/hilbert.h
@@ -1,4 +1,5 @@
 #include <stdlib.h>
+#include <math.h>
 #include "constants.h"
 
 #define D_SIZE 256