diff --git a/sys/dev/evdev/evdev_mt.c b/sys/dev/evdev/evdev_mt.c
--- a/sys/dev/evdev/evdev_mt.c
+++ b/sys/dev/evdev/evdev_mt.c
@@ -101,7 +101,7 @@
 static inline int
 ffc_slot(struct evdev_dev *evdev, slotset_t slots)
 {
-	return (ffs(~slots & (2U << MAXIMAL_MT_SLOT(evdev)) - 1) - 1);
+	return (ffs(~slots & ((2U << MAXIMAL_MT_SLOT(evdev)) - 1)) - 1);
 }
 
 void