diff --git a/quapy/protocol.py b/quapy/protocol.py
index fec37ca..f8b828f 100644
--- a/quapy/protocol.py
+++ b/quapy/protocol.py
@@ -301,7 +301,8 @@ class CovariateShiftPP(AbstractStochasticSeededProtocol):
             repeats=1,
             prevalence=None,
             mixture_points=11,
-            random_seed=None):
+            random_seed=None,
+            return_type='sample_prev'):
         super(CovariateShiftPP, self).__init__(random_seed)
         self.A = domainA
         self.B = domainB
@@ -322,6 +323,7 @@ class CovariateShiftPP(AbstractStochasticSeededProtocol):
             assert all(np.logical_and(self.mixture_points >= 0, self.mixture_points<=1)), \
                 'mixture_model datatype not understood (expected int or a sequence of real values in [0,1])'
         self.random_seed = random_seed
+        self.collator = OnLabelledCollectionProtocol.get_collator(return_type)
 
     def samples_parameters(self):
         indexesA, indexesB = [], []
@@ -339,7 +341,7 @@ class CovariateShiftPP(AbstractStochasticSeededProtocol):
         indexesA, indexesB = indexes
         sampleA = self.A.sampling_from_index(indexesA)
         sampleB = self.B.sampling_from_index(indexesB)
-        return (sampleA+sampleB).Xp
+        return self.collator(sampleA+sampleB)
 
     def total(self):
         return self.repeats * len(self.mixture_points)