diff --git a/mmdet/datasets/transforms/loading.py b/mmdet/datasets/transforms/loading.py
index 722d4b0e7c8..914442a7138 100644
--- a/mmdet/datasets/transforms/loading.py
+++ b/mmdet/datasets/transforms/loading.py
@@ -133,7 +133,7 @@ def transform(self, results: dict) -> dict:
                     img_bytes,
                     flag=self.color_type,
                     backend=self.imdecode_backend))
-        img = np.stack(img, axis=-1)
+        img = np.concatenate(img, axis=-1)
         if self.to_float32:
             img = img.astype(np.float32)