diff --git a/htdocs/langs/en_US/mrp.lang b/htdocs/langs/en_US/mrp.lang
index 9e1c8bb64ce..44fb4457999 100644
--- a/htdocs/langs/en_US/mrp.lang
+++ b/htdocs/langs/en_US/mrp.lang
@@ -82,6 +82,7 @@ ProductsToProduce=Products to produce
 UnitCost=Unit cost
 TotalCost=Total cost
 BOMTotalCost=The cost to produce this BOM based on cost of each quantity and product to consume (use Cost price if defined, else Average Weighted Price if defined, else the Best purchase price)
+BOMTotalCostService=If the "Workstation" module is activated and a workstation is defined by default on the line, then the calculation is "quantity (converted into hours) x workstation ahr", otherwise "quantity (converted into hours) x cost price of the service"
 GoOnTabProductionToProduceFirst=You must first have started the production to close a Manufacturing Order (See tab '%s'). But you can Cancel it.
 ErrorAVirtualProductCantBeUsedIntoABomOrMo=A kit can't be used into a BOM or a MO
 Workstation=Workstation