diff --git a/src/newgrf_industrytiles.h b/src/newgrf_industrytiles.h
--- a/src/newgrf_industrytiles.h
+++ b/src/newgrf_industrytiles.h
@@ -7,5 +7,6 @@
 
 bool DrawNewIndustryTile(TileInfo *ti, Industry *i, IndustryGfx gfx, const IndustryTileSpec *inds);
 uint16 GetIndustryTileCallback(uint16 callback, uint32 param1, uint32 param2, IndustryGfx gfx_id, Industry *industry, TileIndex tile);
+bool PerformIndustryTileSlopeCheck(TileIndex tile, const IndustryTileSpec *its, IndustryGfx gfx);
 
 #endif /* NEWGRF_INDUSTRYTILES_H */