diff --git a/tools/libinput-analyze-per-slot-delta.py b/tools/libinput-analyze-per-slot-delta.py
index e40a7df4..07df3f42 100755
--- a/tools/libinput-analyze-per-slot-delta.py
+++ b/tools/libinput-analyze-per-slot-delta.py
@@ -179,6 +179,7 @@ def main(argv):
         nslots = 1
 
     slots = [Slot(i) for i in range(0, nslots)]
+    slots[0].used = True
 
     marker_button     = "..............."  # noqa