diff --git a/gdbus/mainloop.c b/gdbus/mainloop.c
index 7f2d001..ec10ab0 100644
--- a/gdbus/mainloop.c
+++ b/gdbus/mainloop.c
@@ -347,8 +347,12 @@
 			return FALSE;
 	}
 
-	if (result != DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER)
+	if (result != DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER) {
+		if (error != NULL)
+			dbus_set_error(error, name, "Name already in use");
+
 		return FALSE;
+	}
 
 	return TRUE;
 }