diff --git a/package/x11r7/xapp_xdm/Config.in b/package/x11r7/xapp_xdm/Config.in
index 477cd771cd..69829701ca 100644
--- a/package/x11r7/xapp_xdm/Config.in
+++ b/package/x11r7/xapp_xdm/Config.in
@@ -1,5 +1,6 @@
 config BR2_PACKAGE_XAPP_XDM
 	bool "xdm"
+	depends on BR2_USE_MMU # fork()
 	# Runtime dependency: can't start an X server unless there is one
 	depends on BR2_PACKAGE_XSERVER_XORG_SERVER
 	select BR2_PACKAGE_XAPP_SESSREG