diff --git a/gio/gsimpleproxyresolver.c b/gio/gsimpleproxyresolver.c
index f19d56743..6a97ba2c6 100644
--- a/gio/gsimpleproxyresolver.c
+++ b/gio/gsimpleproxyresolver.c
@@ -415,7 +415,7 @@ g_simple_proxy_resolver_class_init (GSimpleProxyResolverClass *resolver_class)
   object_class->finalize = g_simple_proxy_resolver_finalize;
 
   /**
-   * GSimpleProxyResolver:default-proxy:
+   * GSimpleProxyResolver:default-proxy: (nullable)
    *
    * The default proxy URI that will be used for any URI that doesn't
    * match #GSimpleProxyResolver:ignore-hosts, and doesn't match any
@@ -518,7 +518,7 @@ g_simple_proxy_resolver_new (const gchar  *default_proxy,
 /**
  * g_simple_proxy_resolver_set_default_proxy:
  * @resolver: a #GSimpleProxyResolver
- * @default_proxy: the default proxy to use
+ * @default_proxy: (nullable): the default proxy to use
  *
  * Sets the default proxy on @resolver, to be used for any URIs that
  * don't match #GSimpleProxyResolver:ignore-hosts or a proxy set