diff --git a/gtk/gtkmediafile.c b/gtk/gtkmediafile.c
index 9620220ab8..15aadf9d74 100644
--- a/gtk/gtkmediafile.c
+++ b/gtk/gtkmediafile.c
@@ -643,4 +643,8 @@ gtk_media_file_extension_init (void)
                    g_type_name (g_io_extension_get_type (ext)));
         }
     }
+
+  /* If the env var is given, check at startup that things actually work */
+  if (g_getenv ("GTK_MEDIA"))
+    gtk_media_file_get_extension ();
 }