diff --git a/pigeon_magnet_solver/board.py b/pigeon_magnet_solver/board.py
index e43a69f..8d7add8 100644
--- a/pigeon_magnet_solver/board.py
+++ b/pigeon_magnet_solver/board.py
@@ -89,10 +89,13 @@ class Board:
         old_row = self.rows[row]
         self.rows[row] = old_row[:col] + value + old_row[col+1:]
 
-    def click(self, index: int) -> Self:
+    def click(self, index: int) -> Self | None:
         # check is clickable
         row, col = index // self.width, index % self.width
-        assert self.rows[row][col] == "1", f"{index} is not clickable!"
+
+        if self.rows[row][col] != "1":
+            # button is not clickable
+            return None
 
         # get neighbor positions
         nb_rc = [
diff --git a/tests/test_board.py b/tests/test_board.py
index ba596f3..e3d135e 100644
--- a/tests/test_board.py
+++ b/tests/test_board.py
@@ -1,5 +1,3 @@
-import pytest
-
 from pigeon_magnet_solver.board import Board
 
 
@@ -13,9 +11,11 @@ def test_default():
     assert board.binary_repr == (4, 11, 3), "Wrong binary repr"
     assert board.solution_class == (1, 3, 2), "Wrong solution class"
 
-    assert board.click(4).binary_repr == (4, 14, 3)
-    assert board.click(5).binary_repr == (4, 11, 6)
+    assert (board2 := board.click(4)) is not None
+    assert board2.binary_repr == (4, 14, 3)
+
+    assert (board2 := board.click(5)) is not None
+    assert board2.binary_repr == (4, 11, 6)
 
     for idx in (3, 7):
-        with pytest.raises(AssertionError):
-            board.click(idx)
+        assert board.click(idx) is None