diff --git a/src/hashmap.h b/src/hashmap.h
index 03748a7..e83055e 100644
--- a/src/hashmap.h
+++ b/src/hashmap.h
@@ -10,4 +10,5 @@

 #include <stdbool.h>
 #include <stddef.h>
+#include <bits/reg.h>
 #include "libbpf_internal.h"

 static inline size_t hash_bits(size_t h, int bits)