diff --git a/src/sk_transformers/generic_transformer.py b/src/sk_transformers/generic_transformer.py
index 4fdcc6e..53a550c 100644
--- a/src/sk_transformers/generic_transformer.py
+++ b/src/sk_transformers/generic_transformer.py
@@ -544,7 +544,9 @@ def transform(self, Xy: pd.DataFrame) -> pd.DataFrame:
             pd.DataFrame: Dataframe with the queries applied.
         """
 
-        Xy = check_ready_to_transform(self, Xy, force_all_finite="allow-nan")
+        Xy = check_ready_to_transform(
+            self, Xy, Xy.columns, force_all_finite="allow-nan"
+        )
         for query in self.queries:
             Xy = Xy.query(query, inplace=False)
         return Xy
diff --git a/src/sk_transformers/utils.py b/src/sk_transformers/utils.py
index 248b0f0..5501b15 100644
--- a/src/sk_transformers/utils.py
+++ b/src/sk_transformers/utils.py
@@ -8,7 +8,7 @@
 def check_ready_to_transform(
     transformer: Any,
     X: pd.DataFrame,
-    features: Optional[Union[str, List[str]]] = None,
+    features: Union[str, List[str]],
     force_all_finite: Union[bool, str] = True,
     dtype: Optional[Union[str, List[str]]] = None,
 ) -> pd.DataFrame:
@@ -38,25 +38,25 @@ def check_ready_to_transform(
         pandas.DataFrame: A checked copy of original dataframe.
     """
 
+    if isinstance(features, str):
+        features = [features]
+
     if not isinstance(X, pd.DataFrame):
         raise ValueError("X must be a Pandas dataframe!")
     if X.empty:
         raise ValueError("X must not be empty!")
-    if features:
-        if isinstance(features, str):
-            if not features in X.columns:
-                raise ValueError(f"Column `{features}` not in dataframe!")
-        elif isinstance(features, list):
-            if not all(c in X.columns for c in features):
-                not_in_df = (
-                    str([c for c in features if c not in X.columns])
-                    .replace("[", "")
-                    .replace("]", "")
-                    .replace("'", "`")
-                )
-                raise ValueError(
-                    f"Not all provided `features` could be found in `X`! Following columns were not found in the dataframe: {not_in_df}."
-                )
+
+    if isinstance(features, list):
+        if not all(c in X.columns for c in features):
+            not_in_df = (
+                str([c for c in features if c not in X.columns])
+                .replace("[", "")
+                .replace("]", "")
+                .replace("'", "`")
+            )
+            raise ValueError(
+                f"Not all provided `features` could be found in `X`! Following columns were not found in the dataframe: {not_in_df}."
+            )
 
     if issubclass(transformer.__class__, BaseEstimator) is False:
         raise TypeError(
@@ -67,18 +67,26 @@ def check_ready_to_transform(
         )
     check_is_fitted(transformer, "fitted_")
 
-    X_tmp = check_array(
-        X.to_numpy(),
+    X_tmp = X[
+        dict.fromkeys(X[features]).keys()
+    ].copy()  # `dict.fromkeys` was chosen instead of `set` to maintain the order of the entries.
+
+    X_tmp_array = check_array(
+        X_tmp.to_numpy(),
         dtype=dtype,
         accept_large_sparse=False,
         force_all_finite=force_all_finite,
     )
-    X_tmp = pd.DataFrame(X_tmp, columns=X.columns, index=X.index)
+    X_tmp = pd.DataFrame(X_tmp_array, columns=X_tmp.columns, index=X_tmp.index)
 
-    for column in X.columns:
+    for column in X_tmp.columns:
         X_tmp[column] = X_tmp[column].astype(X[column].dtype)
 
-    return X_tmp.copy()
+    non_included_features = [c for c in X.columns if c not in features]
+    if non_included_features:
+        X_tmp = pd.concat([X_tmp, X[non_included_features]], axis=1)
+
+    return X_tmp
 
 
 def check_data(X: pd.DataFrame, y: pd.Series, check_nans: bool = True) -> None:
diff --git a/tests/test_utils.py b/tests/test_utils.py
index 585c616..07cd2ba 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -13,14 +13,14 @@
 
 def test_check_ready_to_transform_for_empty_df() -> None:
     with pytest.raises(ValueError) as error:
-        check_ready_to_transform(None, pd.DataFrame())
+        check_ready_to_transform(None, pd.DataFrame(), ["a"])
 
     assert "X must not be empty!" == str(error.value)
 
 
 def test_check_ready_to_transform_for_not_dataframe() -> None:
     with pytest.raises(ValueError) as error:
-        check_ready_to_transform(None, np.ndarray([1, 2, 3]))
+        check_ready_to_transform(None, np.ndarray([1, 2, 3]), ["a"])
 
     assert "X must be a Pandas dataframe!" == str(error.value)
 
@@ -29,7 +29,10 @@ def test_check_ready_to_transform_for_wrong_column() -> None:
     with pytest.raises(ValueError) as error:
         check_ready_to_transform(None, pd.DataFrame({"a": [1, 2, 3]}), "b")
 
-    assert "Column `b` not in dataframe!" == str(error.value)
+    assert (
+        "Not all provided `features` could be found in `X`! Following columns were not found in the dataframe: `b`."
+        == str(error.value)
+    )
 
 
 def test_check_ready_to_transform_for_wrong_columns() -> None: