diff --git a/ema_workbench/em_framework/callbacks.py b/ema_workbench/em_framework/callbacks.py
index e07768190..dbebbc282 100644
--- a/ema_workbench/em_framework/callbacks.py
+++ b/ema_workbench/em_framework/callbacks.py
@@ -219,7 +219,7 @@ def __init__(
                 ("model", "object"),
             ]
         )
-
+        self.dtypes = dtypes
         self.cases = np.empty(nr_experiments, dtype=dtypes)
 
         for outcome in self.outcomes: