diff --git a/python/python/python.conf b/python/python/python.conf
index 5cf777b46..5214120a0 100644
--- a/python/python/python.conf
+++ b/python/python/python.conf
@@ -55,4 +55,6 @@ fix_python_for_64bit() {
 # cross-compiling tweaks
 if atstage cross; then
 	var_append configcache ' ' "ac_cv_buggy_getaddrinfo=no"
+	# on a running system we have /dev/ptmx
+	var_append configcache ' ' "ac_cv_file__dev_ptmx=yes"
 fi