diff --git a/src/main.rs b/src/main.rs
index 8a625a2..3ac0cb2 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -92,10 +92,15 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
                     if let Some(i) = state.selected()
                         && i < marked.len()
                     {
-                        marked[i] = true;
-                        // move cursor down
-                        let next = if i + 1 < lines.len() { i + 1 } else { i };
-                        state.select(Some(next));
+                        assert!(i < marked.len());
+                        if marked[i] {
+                            marked[i] = false;
+                        } else {
+                            marked[i] = true;
+                            // move cursor down
+                            let next = lines.len().min(i + 1);
+                            state.select(Some(next));
+                        }
                     }
                 }
                 _ => {}