diff --git a/lisgd.c b/lisgd.c
index e3a1c1c..9d3442b 100644
--- a/lisgd.c
+++ b/lisgd.c
@@ -169,6 +169,7 @@ touchup(struct libinput_event *e)
 void
 run()
 {
+	int i;
 	struct libinput *li;
 	struct libinput_event *event;
 	struct libinput_event_touch *tevent;
@@ -191,6 +192,14 @@ run()
 		die("Couldn't set mode to capture events\n");
 	}
 
+	// E.g. initially invalidate every slot 
+	for (i = 0; i < MAXSLOTS; i++) {
+		xend[i] = INVALID;
+		yend[i] = INVALID;
+		xstart[i] = INVALID;
+		ystart[i] = INVALID;
+	}
+
 	FD_ZERO(&fdset);
 	FD_SET(libinput_get_fd(li), &fdset);
 	for (;;) {