diff --git a/backend/engine/engine.py b/backend/engine/engine.py
index 04860add..db3b6d0d 100644
--- a/backend/engine/engine.py
+++ b/backend/engine/engine.py
@@ -877,7 +877,10 @@ async def model_engine(body: PlanTriggerRequest):
                 else:
 
                     if body.budget:
-                        optimiser = GainOptimiser(input_measures, max_cost=body.budget, max_gain=gain)
+                        optimiser = GainOptimiser(
+                            input_measures, max_cost=body.budget, max_gain=gain,
+                            allow_slack=body.goal == "Increasing EPC"
+                        )
                     else:
                         # The minimum gain is the minimum number of SAP points required to get to the target SAP band
                         # If the gain is negative, the optimiser will return an empty solution