1 files changed, 5 insertions, 0 deletions
diff --git a/util.h b/util.h
index 0a87c0c..4aedcd9 100644
--- a/util.h
+++ b/util.h
@@ -1,3 +1,6 @@
+#ifndef UTIL_H_
+#define UTIL_H_
+
 #include <stdarg.h>
 #include <stddef.h>
 #include <stdlib.h>
@@ -44,3 +47,5 @@ static uint8_t popcount64(uint64_t x) {
 	}
 	return cnt;
 }
+
+#endif