diff --git a/dynophores/core/superfeature.py b/dynophores/core/superfeature.py
index 39a6db9..c2fc7a0 100644
--- a/dynophores/core/superfeature.py
+++ b/dynophores/core/superfeature.py
@@ -184,7 +184,7 @@ def _count(self, property_envpartners_occurrences):
         )
         envpartners_count = property_envpartners_occurrences.sum()
 
-        return superfeature_count.append(envpartners_count)
+        return pd.concat([superfeature_count, envpartners_count])
 
     @property
     def frequency(self):