diff --git a/test/test-libevdev-events.c b/test/test-libevdev-events.c
index de598f9..50f5fcc 100644
--- a/test/test-libevdev-events.c
+++ b/test/test-libevdev-events.c
@@ -909,7 +909,7 @@ START_TEST(test_syn_delta_tracking_ids)
 	abs[3].maximum = 1000;
 
 	abs[4].value = ABS_MT_SLOT;
-	abs[4].maximum = num_slots - 1;
+	abs[4].maximum = num_slots;
 
 	abs[5].minimum = -1;
 	abs[5].maximum = 255;