diff --git a/src/ssl_sock.c b/src/ssl_sock.c
index 0f18132b1..a81688309 100644
--- a/src/ssl_sock.c
+++ b/src/ssl_sock.c
@@ -4462,7 +4462,7 @@ static void ssl_set_shctx(SSL_CTX *ctx)
 static void SSL_CTX_keylog(const SSL *ssl, const char *line)
 {
 	struct ssl_keylog *keylog;
-	char *lastarg = NULL;
+	const char *lastarg = NULL;
 	char *dst = NULL;
 
 #ifdef USE_QUIC_OPENSSL_COMPAT