diff --git a/src/corridorkey_mlx/inference/tiling.py b/src/corridorkey_mlx/inference/tiling.py
index 1591385..84be576 100644
--- a/src/corridorkey_mlx/inference/tiling.py
+++ b/src/corridorkey_mlx/inference/tiling.py
@@ -27,6 +27,10 @@ def _compute_tile_coords(
 
     Tiles overlap by `overlap` pixels. Last tile is clamped to image boundary.
     """
+    if overlap >= tile_size:
+        msg = f"overlap ({overlap}) must be less than tile_size ({tile_size})"
+        raise ValueError(msg)
+
     if image_size <= tile_size:
         return [(0, image_size)]
 
diff --git a/tests/test_tiling_consistency.py b/tests/test_tiling_consistency.py
index 5bf0499..c467e2c 100644
--- a/tests/test_tiling_consistency.py
+++ b/tests/test_tiling_consistency.py
@@ -32,6 +32,12 @@ def model() -> GreenFormer:
 
 
 class TestTileCoords:
+    def test_overlap_gte_tile_size_raises(self) -> None:
+        with pytest.raises(ValueError, match="overlap.*must be less than tile_size"):
+            _compute_tile_coords(512, 256, 256)
+        with pytest.raises(ValueError, match="overlap.*must be less than tile_size"):
+            _compute_tile_coords(512, 256, 300)
+
     def test_single_tile(self) -> None:
         coords = _compute_tile_coords(200, 256, 32)
         assert coords == [(0, 200)]