diff --git a/src/order_cmd.cpp b/src/order_cmd.cpp
index f6ad069995..d6e1748f90 100644
--- a/src/order_cmd.cpp
+++ b/src/order_cmd.cpp
@@ -1849,7 +1849,7 @@ void DeleteVehicleOrders(Vehicle *v, bool keep_orderlist, bool reset_order_indic
  * @param interval proposed service interval
  * @return Clamped service interval
  */
-uint16_t GetServiceIntervalClamped(uint interval, bool ispercent)
+uint16_t GetServiceIntervalClamped(int interval, bool ispercent)
 {
 	return ispercent ? Clamp(interval, MIN_SERVINT_PERCENT, MAX_SERVINT_PERCENT) : Clamp(interval, MIN_SERVINT_DAYS, MAX_SERVINT_DAYS);
 }
diff --git a/src/order_func.h b/src/order_func.h
index c879a2a30d..f8771b09dc 100644
--- a/src/order_func.h
+++ b/src/order_func.h
@@ -37,6 +37,6 @@ static const uint DEF_SERVINT_PERCENT = 50;
 static const uint MIN_SERVINT_PERCENT = 5;
 static const uint MAX_SERVINT_PERCENT = 90;
 
-uint16_t GetServiceIntervalClamped(uint interval, bool ispercent);
+uint16_t GetServiceIntervalClamped(int interval, bool ispercent);
 
 #endif /* ORDER_FUNC_H */