diff --git a/src/postprocessor/core/reshapers/picker.py b/src/postprocessor/core/reshapers/picker.py
index 11879bd5e270c9d45b2a8f1c87fd8a136064d91d..747623eea6a16186ed53016ac66f3bd78947d77b 100644
--- a/src/postprocessor/core/reshapers/picker.py
+++ b/src/postprocessor/core/reshapers/picker.py
@@ -102,8 +102,8 @@ class picker(LineageProcess):
             self.daughters = np.array([])
         else:
             self.mothers, self.daughters = (
-                self.cells.mothers_daughters[:, 1],
-                self.cells.mothers_daughters[:, 2],
+                tuple(self.cells.mothers_daughters[:, 1]),
+                tuple(self.cells.mothers_daughters[:, 2]),
             )
         for alg, op, *params in self.sequence:
             if indices: