diff --git a/flexmeasures/data/models/reporting/pandas_reporter.py b/flexmeasures/data/models/reporting/pandas_reporter.py
index 1802fe9a16..ff3bbb403f 100644
--- a/flexmeasures/data/models/reporting/pandas_reporter.py
+++ b/flexmeasures/data/models/reporting/pandas_reporter.py
@@ -349,8 +349,14 @@ def _any_empty(objs):
             if (_any_empty(args) or _any_empty(kwargs.values())) and skip_if_empty:
                 self.data[df_output] = self.data[df_input]
             else:
-                self.data[df_output] = getattr(self.data[df_input], method)(
-                    *args, **kwargs
-                )
+                try:
+                    self.data[df_output] = getattr(self.data[df_input], method)(
+                        *args, **kwargs
+                    )
+                except TypeError as exc:
+                    if "unhashable type" in str(exc) and method == "sum":
+                        raise TypeError(
+                            "Consider using 'add' instead of 'sum' as the transformation method."
+                        ) from exc
 
             previous_df = df_output