diff --git a/src/landscape.h b/src/landscape.h
--- a/src/landscape.h
+++ b/src/landscape.h
@@ -26,6 +26,7 @@ bool IsValidTile(TileIndex tile);
 uint GetPartialZ(int x, int y, Slope corners);
 uint GetSlopeZ(int x, int y);
 void GetSlopeZOnEdge(Slope tileh, DiagDirection edge, int *z1, int *z2);
+int GetSlopeZInCorner(Slope tileh, Corner corner);
 
 static inline Point RemapCoords(int x, int y, int z)
 {