diff --git a/Scripts/assignment/mock_assignment.py b/Scripts/assignment/mock_assignment.py
index 2992eceb..b8edee69 100644
--- a/Scripts/assignment/mock_assignment.py
+++ b/Scripts/assignment/mock_assignment.py
@@ -157,10 +157,9 @@ def _get_matrices(self,
             Subtype (car_work/truck/inv_time/...) : numpy 2-d matrix
                 Matrix of the specified type
         """
-        matrix_list = [ass_class for ass_class in assignment_classes
-            if mtx_type in param.emme_matrices.get(ass_class, [])]
         with self.matrices.open(
-                mtx_type, self.name, transport_classes=matrix_list) as mtx:
+                mtx_type, self.name, transport_classes=[]) as mtx:
+            matrix_list = set(assignment_classes) & set(mtx.matrix_list)
             matrices = {mode: mtx[mode] for mode in matrix_list}
         for mode in matrices:
             if numpy.any(matrices[mode] > 1e10):