diff --git a/basicsr/data/paired_image_dataset.py b/basicsr/data/paired_image_dataset.py
index 9f5c8c6ad..2f4235acc 100644
--- a/basicsr/data/paired_image_dataset.py
+++ b/basicsr/data/paired_image_dataset.py
@@ -96,7 +96,7 @@ def __getitem__(self, index):
         # BGR to RGB, HWC to CHW, numpy to tensor
         img_gt, img_lq = img2tensor([img_gt, img_lq], bgr2rgb=True, float32=True)
         # normalize
-        if self.mean is not None or self.std is not None:
+        if self.mean is not None and self.std is not None:
             normalize(img_lq, self.mean, self.std, inplace=True)
             normalize(img_gt, self.mean, self.std, inplace=True)