diff --git a/activitysim/examples/prototype_mtc_extended/configs/tour_mode_choice.yaml b/activitysim/examples/prototype_mtc_extended/configs/tour_mode_choice.yaml
index 19f5014fc..6550c28e5 100644
--- a/activitysim/examples/prototype_mtc_extended/configs/tour_mode_choice.yaml
+++ b/activitysim/examples/prototype_mtc_extended/configs/tour_mode_choice.yaml
@@ -196,3 +196,6 @@ LOGSUM_CHOOSER_COLUMNS:
 
 
 MODE_CHOICE_LOGSUM_COLUMN_NAME: mode_choice_logsum
+
+compute_settings:
+  fastmath: false  # use of isnan in utility functions requires fastmath=False