diff --git a/mmdet3d/models/middle_encoders/pillar_scatter.py b/mmdet3d/models/middle_encoders/pillar_scatter.py
index 725ce290f..029aa90e4 100644
--- a/mmdet3d/models/middle_encoders/pillar_scatter.py
+++ b/mmdet3d/models/middle_encoders/pillar_scatter.py
@@ -39,7 +39,7 @@ def forward_single(self, voxel_features, coors):
         """Scatter features of single sample.
 
         Args:
-            voxel_features (torch.Tensor): Voxel features in shape (N, M, C).
+            voxel_features (torch.Tensor): Voxel features in shape (N, C).
             coors (torch.Tensor): Coordinates of each voxel.
                 The first column indicates the sample ID.
         """
@@ -63,7 +63,7 @@ def forward_batch(self, voxel_features, coors, batch_size):
         """Scatter features of single sample.
 
         Args:
-            voxel_features (torch.Tensor): Voxel features in shape (N, M, C).
+            voxel_features (torch.Tensor): Voxel features in shape (N, C).
             coors (torch.Tensor): Coordinates of each voxel in shape (N, 4).
                 The first column indicates the sample ID.
             batch_size (int): Number of samples in the current batch.