diff --git a/src/newgrf_industrytiles.h b/src/newgrf_industrytiles.h
--- a/src/newgrf_industrytiles.h
+++ b/src/newgrf_industrytiles.h
@@ -27,7 +27,7 @@ enum IndustryAnimationTrigger {
 
 bool DrawNewIndustryTile(TileInfo *ti, Industry *i, IndustryGfx gfx, const IndustryTileSpec *inds);
 uint16 GetIndustryTileCallback(CallbackID callback, uint32 param1, uint32 param2, IndustryGfx gfx_id, Industry *industry, TileIndex tile);
-bool PerformIndustryTileSlopeCheck(TileIndex ind_base_tile, TileIndex ind_tile, const IndustryTileSpec *its, IndustryType type, IndustryGfx gfx, uint itspec_index);
+CommandCost PerformIndustryTileSlopeCheck(TileIndex ind_base_tile, TileIndex ind_tile, const IndustryTileSpec *its, IndustryType type, IndustryGfx gfx, uint itspec_index);
 
 void AnimateNewIndustryTile(TileIndex tile);
 bool StartStopIndustryTileAnimation(TileIndex tile, IndustryAnimationTrigger iat, uint32 random = Random());