diff --git a/bob/pipelines/mixins.py b/bob/pipelines/mixins.py
index 1976b1ae50e3b22c220b7e93d483051b34595a61..46683c5fdf2665c4789ba81bcd93606c1e298a0b 100644
--- a/bob/pipelines/mixins.py
+++ b/bob/pipelines/mixins.py
@@ -245,7 +245,7 @@ class SampleMixin(BaseEstimator):
         # See: https://scikit-learn.org/stable/developers/develop.html
         # if the estimator does not require fit or is stateless don't call fit
         tags = self._get_tags()
-        if tags["stateless"] or not tags["requires_fit"]:
+        if tags["stateless"] or ("requires_fit" in tags and not tags["requires_fit"]):
             return self
 
         # if the estimator needs to be fitted.