diff --git a/src/libsodium/include/sodium/crypto_secretbox_xsalsa20poly1305.h b/src/libsodium/include/sodium/crypto_secretbox_xsalsa20poly1305.h
index 338347c5..99e760f8 100644
--- a/src/libsodium/include/sodium/crypto_secretbox_xsalsa20poly1305.h
+++ b/src/libsodium/include/sodium/crypto_secretbox_xsalsa20poly1305.h
@@ -45,7 +45,8 @@ int crypto_secretbox_xsalsa20poly1305_open(unsigned char *m,
                                            const unsigned char *c,
                                            unsigned long long clen,
                                            const unsigned char *n,
-                                           const unsigned char *k);
+                                           const unsigned char *k)
+            __attribute__ ((warn_unused_result));
 
 #ifdef __cplusplus
 }