diff --git a/rota_generator/shifts.py b/rota_generator/shifts.py
index da5c53f..a479e2c 100644
--- a/rota_generator/shifts.py
+++ b/rota_generator/shifts.py
@@ -2788,18 +2788,19 @@ class RotaBuilder(object):
                             "target_shifts": target_shifts,
                         }
 
-                        self.model.constraints.add(
-                            inequality(
-                                min_shifts,
-                                sum(
-                                    self.model.works[worker.id, week, day, shift.name]
-                                    for week, day in self.get_week_day_combinations_for_shift(
-                                        shift
-                                    )
-                                ),
-                                max_shifts,
+                        if self.get_week_day_combinations_for_shift(shift):
+                            self.model.constraints.add(
+                                inequality(
+                                    min_shifts,
+                                    sum(
+                                        self.model.works[worker.id, week, day, shift.name]
+                                        for week, day in self.get_week_day_combinations_for_shift(
+                                            shift
+                                        )
+                                    ),
+                                    max_shifts,
+                                )
                             )
-                        )
                 else:
                     # Make sure shifts aren't assigned to those from other sites
                     # Not needed if there are no shifts