diff --git a/src/libsodium/crypto_box/curve25519xsalsa20poly1305/ref/box_curve25519xsalsa20poly1305.c b/src/libsodium/crypto_box/curve25519xsalsa20poly1305/ref/box_curve25519xsalsa20poly1305.c
index 63b5be39..ebc208a3 100644
--- a/src/libsodium/crypto_box/curve25519xsalsa20poly1305/ref/box_curve25519xsalsa20poly1305.c
+++ b/src/libsodium/crypto_box/curve25519xsalsa20poly1305/ref/box_curve25519xsalsa20poly1305.c
@@ -1,4 +1,5 @@
 #include "api.h"
+#include "utils.h"
 
 int crypto_box(
   unsigned char *c,