diff --git a/src/libudev/libudev-enumerate.c b/src/libudev/libudev-enumerate.c
index 7e63820cb..77f75bfd3 100644
--- a/src/libudev/libudev-enumerate.c
+++ b/src/libudev/libudev-enumerate.c
@@ -718,6 +718,8 @@ static bool match_subsystem(struct udev_enumerate *udev_enumerate, const char *s
 {
         struct udev_list_entry *list_entry;
 
+        subsystem = subsystem ? : "";
+
         udev_list_entry_foreach(list_entry, udev_list_get_entry(&udev_enumerate->subsystem_nomatch_list)) {
                 if (fnmatch(udev_list_entry_get_name(list_entry), subsystem, 0) == 0)
                         return false;