diff --git a/gio/tests/gdbus-peer.c b/gio/tests/gdbus-peer.c
index 841c40cda..081eef6f5 100644
--- a/gio/tests/gdbus-peer.c
+++ b/gio/tests/gdbus-peer.c
@@ -646,7 +646,7 @@ read_all_from_fd (gint fd, gsize *out_len, GError **error)
 
  error:
   if (out_len != NULL)
-    out_len = 0;
+    *out_len = 0;
   g_string_free (str, TRUE);
   return NULL;
 }