diff --git a/src/bonsai/bonsai/bim/module/cost/operator.py b/src/bonsai/bonsai/bim/module/cost/operator.py
index 79338d5ede..9dfe4c20fd 100644
--- a/src/bonsai/bonsai/bim/module/cost/operator.py
+++ b/src/bonsai/bonsai/bim/module/cost/operator.py
@@ -695,6 +695,10 @@ class ExportCostSchedules(bpy.types.Operator, ExportHelper):
         default=True,
     )
 
+    @property
+    def filename_ext(self) -> str:
+        return f".{self.format.lower()}"
+
     def execute(self, context):
         cost_schedule = tool.Ifc.get().by_id(self.cost_schedule) if self.cost_schedule else None
         r = core.export_cost_schedules(