diff --git a/src/udev/udev-builtin.c b/src/udev/udev-builtin.c
index fbed496c4e..de284d60fe 100644
--- a/src/udev/udev-builtin.c
+++ b/src/udev/udev-builtin.c
@@ -105,7 +105,9 @@ UdevBuiltinCommand udev_builtin_lookup(const char *command) {
         command += strspn(command, WHITESPACE);
         n = strcspn(command, WHITESPACE);
         for (UdevBuiltinCommand i = 0; i < _UDEV_BUILTIN_MAX; i++)
-                if (builtins[i] && strneq(builtins[i]->name, command, n))
+                if (builtins[i] &&
+                    strlen(builtins[i]->name) == n &&
+                    strneq(builtins[i]->name, command, n))
                         return i;
 
         return _UDEV_BUILTIN_INVALID;
diff --git a/test/units/TEST-17-UDEV.sanity-check.sh b/test/units/TEST-17-UDEV.sanity-check.sh
index 18326c03ad..c0bd2b1565 100755
--- a/test/units/TEST-17-UDEV.sanity-check.sh
+++ b/test/units/TEST-17-UDEV.sanity-check.sh
@@ -178,6 +178,8 @@ udevadm test -h
 
 # Builtins
 (! udevadm test-builtin aaaaa /dev/null)
+(! udevadm test-builtin k /dev/null)
+(! udevadm test-builtin key /dev/null)
 udevadm test-builtin blkid "$loopdev"
 (! udevadm test-builtin "btrfs" "$loopdev")
 (! udevadm test-builtin "btrfs aaaaa" "$loopdev")