diff --git a/gio/gdbusauthmechanismexternal.c b/gio/gdbusauthmechanismexternal.c
index 38a2f6500..f0bcfc349 100644
--- a/gio/gdbusauthmechanismexternal.c
+++ b/gio/gdbusauthmechanismexternal.c
@@ -325,7 +325,7 @@ mechanism_client_initiate (GDBusAuthMechanism   *mechanism,
                            gsize                *out_initial_response_len)
 {
   GDBusAuthMechanismExternal *m = G_DBUS_AUTH_MECHANISM_EXTERNAL (mechanism);
-  gchar *initial_response;
+  gchar *initial_response = NULL;
   GCredentials *credentials;
 
   g_return_val_if_fail (G_IS_DBUS_AUTH_MECHANISM_EXTERNAL (mechanism), NULL);