diff --git a/src/lib.rs b/src/lib.rs
index da7e71a..18bd36e 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -213,6 +213,10 @@ impl State {
             Cell::Box | Cell::Goal(true) => {
                 let bpos = dpos + pos;
 
+                if ((bpos.1 * self.lvl.size.0) + bpos.0) as usize >= self.lvl.map.len() {
+                    return Err(Error::BadMove(bpos));
+                }
+
                 match self.lvl[bpos] {
                     Cell::None => {
                         self.toggle_box(dpos);