diff --git a/cfg/gtk.cfg b/cfg/gtk.cfg
index 0859db1a6..30413a953 100644
--- a/cfg/gtk.cfg
+++ b/cfg/gtk.cfg
@@ -887,8 +887,13 @@
   <function name="g_object_ref">
     <noreturn>false</noreturn>
   </function>
+  <!-- void g_object_unref (gpointer object); -->
   <function name="g_object_unref">
     <noreturn>false</noreturn>
+    <returnValue type="void"/>
+    <arg nr="1">
+      <not-bool/>
+    </arg>
   </function>
   <function name="g_array_append_vals">
     <leak-ignore/>