diff --git a/src/plugins/irc/irc-sasl.c b/src/plugins/irc/irc-sasl.c
index 3518cb98e..918db03b5 100644
--- a/src/plugins/irc/irc-sasl.c
+++ b/src/plugins/irc/irc-sasl.c
@@ -292,6 +292,7 @@ irc_sasl_mechanism_ecdsa_nist256p_challenge (struct t_irc_server *server,
         if (answer_base64)
             weechat_string_encode_base64 (string, length, answer_base64);
         free (string);
+        string = NULL;
     }
 
     if (string)