diff --git a/PySDM/state/particles.py b/PySDM/state/particles.py
index a35f604cb..2c158ef6d 100644
--- a/PySDM/state/particles.py
+++ b/PySDM/state/particles.py
@@ -70,7 +70,6 @@ def reset_cell_idx(self):
         self.cell_idx.reset_index()
         self.__sort_by_cell_id()
 
-    @property
     def keys(self):
         return self.attributes.keys()