diff --git a/mmeval/metrics/ms_ssim.py b/mmeval/metrics/ms_ssim.py
index 765bdade..b8f06d58 100644
--- a/mmeval/metrics/ms_ssim.py
+++ b/mmeval/metrics/ms_ssim.py
@@ -97,8 +97,8 @@ def add(self, predictions: Sequence[np.ndarray], groundtruths: Sequence[np.ndarr
                 Defaults to None.
         """
         assert len(predictions) == len(groundtruths), (
-            'The length of \'predictions\' and \'groundtruths\' must be '
-            'same.')
+            'The length of "predictions" and "groundtruths" must be '
+            'the same.')
         half1, half2 = predictions, groundtruths
 
         half1 = [reorder_image(samp, self.input_order) for samp in half1]