diff --git a/tests/unit_tests/openvpn/siphash_openssl.h b/tests/unit_tests/openvpn/siphash_openssl.h
index 49c6a9d..a44457e 100644
--- a/tests/unit_tests/openvpn/siphash_openssl.h
+++ b/tests/unit_tests/openvpn/siphash_openssl.h
@@ -60,5 +60,5 @@
  *
  */
 bool
-siphash_openssl_available(void *sip_context);
+siphash_openssl_available(const void *sip_context);
 #endif /* ifndef SIPHASH_OPENSSL_H */