diff --git a/skcriteria/core/dominance.py b/skcriteria/core/dominance.py
index 37e364d..af9b1ef 100644
--- a/skcriteria/core/dominance.py
+++ b/skcriteria/core/dominance.py
@@ -251,8 +251,8 @@ def compare(self, a0, a1):
             ]
         )
 
-        df = df.assign(
-            Performance=[performance_a0, performance_a1, eq],
+        df["Performance"] = pd.Series(
+            [performance_a0, performance_a1, eq], index=df.index
         )
 
         return df
diff --git a/skcriteria/extend.py b/skcriteria/extend.py
index a19dfa8..e38f7a3 100644
--- a/skcriteria/extend.py
+++ b/skcriteria/extend.py
@@ -125,7 +125,7 @@ def mkagg(maybe_func=None, **hparams):
 
         The decorated function should receive the parameters 'matrix',
         'objectives', 'weights', 'dtypes', 'alternatives', 'criteria',
-        'hparams', or **kwargs.
+        'hparams', or kwargs.
 
         Additionally, it should return an array with rankings for each
         alternative and an optional dictionary with calculations that you wish
@@ -220,10 +220,10 @@ def mktransformer(maybe_func=None, **hparams):
 
         The decorated function should receive the parameters 'matrix',
         'objectives', 'weights', 'dtypes', 'alternatives', 'criteria',
-        'hparams', or **kwargs.
+        'hparams', or kwargs.
 
         In addition, it must return a dictionary whose keys are some
-        as the received parameters (including the keys in '**kwargs').
+        as the received parameters (including the keys in 'kwargs').
         These values replace those of the original array.
         If you return 'hparams,' the transformer will ignore it.
 
diff --git a/skcriteria/utils/rank.py b/skcriteria/utils/rank.py
index 862afa4..69b8c1d 100644
--- a/skcriteria/utils/rank.py
+++ b/skcriteria/utils/rank.py
@@ -64,7 +64,7 @@ def rank_values(arr, reverse=False):
     """
     if reverse:
         arr = np.multiply(arr, -1)
-    return stats.rankdata(arr, "dense").astype(int)
+    return stats.rankdata(arr, "dense").astype(np.int64)
 
 
 # =============================================================================