diff --git a/torchrl/envs/transforms/transforms.py b/torchrl/envs/transforms/transforms.py
index f56701c390d..16f0be8998f 100644
--- a/torchrl/envs/transforms/transforms.py
+++ b/torchrl/envs/transforms/transforms.py
@@ -2080,7 +2080,9 @@ def __init__(
     ):
         if in_keys is None:
             in_keys = IMAGE_KEYS
-        super(GrayScale, self).__init__(in_keys=in_keys, out_keys=out_keys)
+        if out_keys is None:
+            out_keys = copy(in_keys)
+        super().__init__(in_keys=in_keys, out_keys=out_keys)
 
     def _apply_transform(self, observation: torch.Tensor) -> torch.Tensor:
         observation = F.rgb_to_grayscale(observation)