diff --git a/src/llamafactory/data/collator.py b/src/llamafactory/data/collator.py
index 5e67899b..968d7018 100644
--- a/src/llamafactory/data/collator.py
+++ b/src/llamafactory/data/collator.py
@@ -93,7 +93,7 @@ class MultiModalDataCollatorForSeq2Seq(DataCollatorForSeq2Seq):
                 else:
                     image_grid_thw.append(torch.tensor(feature["image_grid_thw"], dtype=torch.long))
 
-            extra_features["image_grid_thw"] = torch.cat(pixel_values, dim=0)
+            extra_features["image_grid_thw"] = torch.cat(image_grid_thw, dim=0)
             if extra_features["image_grid_thw"].numel() == 0:
                 extra_features["image_grid_thw"] = None