diff --git a/embeddings.py b/embeddings.py
index 618f478..fb993d3 100644
--- a/embeddings.py
+++ b/embeddings.py
@@ -174,6 +174,8 @@ def get_3d_rotary_pos_embed(
         grid_t = np.arange(temporal_size, dtype=np.float32)
         grid_t = np.linspace(0, temporal_size, temporal_size, endpoint=False, dtype=np.float32)
     elif grid_type == "slice":
+        if max_size is None:
+            raise ValueError("`max_size` must be provided when `grid_type` is 'slice'")
         max_h, max_w = max_size
         grid_size_h, grid_size_w = grid_size
         grid_h = np.arange(max_h, dtype=np.float32)