diff --git a/src/bn.c b/src/bn.c
index cde0df90..75d187ae 100644
--- a/src/bn.c
+++ b/src/bn.c
@@ -10,6 +10,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <stdint.h>
 #include <string.h>
 #include <assert.h>
 #include <gmssl/endian.h>