--- a/src/newgrf_callbacks.h
+++ b/src/newgrf_callbacks.h
@@ -211,7 +211,7 @@
 	CBID_HOUSE_WATCHED_CARGO_ACCEPTED    = 0x148, // 15 bit callback, not implemented
 
 	/** Callback done for each tile of a station to check the slope. */
-	CBID_STATION_LAND_SLOPE_CHECK        = 0x149, // 15 bit callback, not implemented
+	CBID_STATION_LAND_SLOPE_CHECK        = 0x149, // 15 bit callback
 
 	/** Called to determine the colour of an industry. */
 	CBID_INDUSTRY_DECIDE_COLOUR          = 0x14A, // 4 bit callback

--- a/src/newgrf_commons.cpp
+++ b/src/newgrf_commons.cpp
@@ -413,9 +413,10 @@
  * @param parameter The NewGRF "encoded" offset.
  * @param tile The tile to base the offset from.
  * @param signed_offsets Whether the offsets are to be interpreted as signed or not.
+ * @param axis Axis of a railways station.
  * @return The tile at the offset.
  */
-TileIndex GetNearbyTile(byte parameter, TileIndex tile, bool signed_offsets)
+TileIndex GetNearbyTile(byte parameter, TileIndex tile, bool signed_offsets, Axis axis)
 {
 	int8 x = GB(parameter, 0, 4);
 	int8 y = GB(parameter, 4, 4);
@@ -424,7 +425,8 @@
 	if (signed_offsets && y >= 8) y -= 16;
 
 	/* Swap width and height depending on axis for railway stations */
-	if (HasStationTileRail(tile) && GetRailStationAxis(tile) == AXIS_Y) Swap(x, y);
+	if (axis == INVALID_AXIS && HasStationTileRail(tile)) axis = GetRailStationAxis(tile);
+	if (axis == AXIS_Y) Swap(x, y);
 
 	/* Make sure we never roam outside of the map, better wrap in that case */
 	return TILE_MASK(tile + TileDiffXY(x, y));

--- a/src/newgrf_commons.h
+++ b/src/newgrf_commons.h
@@ -20,6 +20,7 @@
 #include "core/alloc_type.hpp"
 #include "core/smallvec_type.hpp"
 #include "command_type.h"
+#include "direction_type.h"
 
 /** Context for tile accesses */
 enum TileContext {
@@ -266,7 +267,7 @@
 extern ObjectOverrideManager _object_mngr;
 
 uint32 GetTerrainType(TileIndex tile, TileContext context = TCX_NORMAL);
-TileIndex GetNearbyTile(byte parameter, TileIndex tile, bool signed_offsets = true);
+TileIndex GetNearbyTile(byte parameter, TileIndex tile, bool signed_offsets = true, Axis axis = INVALID_AXIS);
 uint32 GetNearbyTileInformation(TileIndex tile);
 CommandCost GetErrorMessageFromLocationCallbackResult(uint16 cb_res, uint32 grfid, StringID default_error);
 

--- a/src/newgrf_spritegroup.h
+++ b/src/newgrf_spritegroup.h
@@ -334,6 +334,7 @@
 			struct BaseStation *st;
 			const struct StationSpec *statspec;
 			CargoID cargo_type;
+			Axis axis;                     ///< Station axis, used only for the slope check callback.
 		} station;
 		struct {
 			TileIndex tile;

--- a/src/newgrf_station.cpp
+++ b/src/newgrf_station.cpp
@@ -279,7 +279,7 @@
 	}
 
 	if (st == NULL) {
-		/* Station does not exist, so we're in a purchase list */
+		/* Station does not exist, so we're in a purchase list or the land slope check callback. */
 		switch (variable) {
 			case 0x40:
 			case 0x41:
@@ -289,6 +289,17 @@
 			case 0x42: return 0;                // Rail type (XXX Get current type from GUI?)
 			case 0x43: return _current_company; // Station owner
 			case 0x44: return 2;                // PBS status
+			case 0x67: // Land info of nearby tile
+				if (object->u.station.axis != INVALID_AXIS && tile != INVALID_TILE) {
+					if (parameter != 0) tile = GetNearbyTile(parameter, tile, true, object->u.station.axis); // only perform if it is required
+
+					Slope tileh = GetTileSlope(tile, NULL);
+					bool swap = (object->u.station.axis == AXIS_Y && HasBit(tileh, CORNER_W) != HasBit(tileh, CORNER_E));
+
+					return GetNearbyTileInformation(tile) ^ (swap ? SLOPE_EW : 0);
+				}
+				break;
+
 			case 0xFA: return Clamp(_date - DAYS_TILL_ORIGINAL_BASE_YEAR, 0, 65535); // Build date, clamped to a 16 bit value
 		}
 
@@ -544,6 +555,7 @@
 	res->u.station.st       = st;
 	res->u.station.statspec = statspec;
 	res->u.station.tile     = tile;
+	res->u.station.axis     = INVALID_AXIS;
 
 	res->callback        = CBID_NO_CALLBACK;
 	res->callback_param1 = 0;
@@ -653,6 +665,39 @@
 	return group->GetCallbackResult();
 }
 
+/**
+ * Check the slope of a tile of a new station.
+ * @param north_tile Norther tile of the station rect.
+ * @param cur_tile Tile to check.
+ * @param statspec Station spec.
+ * @param axis Axis of the new station.
+ * @param plat_len Platform length.
+ * @param numtracks Number of platforms.
+ * @return Succeeded or failed command.
+ */
+CommandCost PerformStationTileSlopeCheck(TileIndex north_tile, TileIndex cur_tile, const StationSpec *statspec, Axis axis, byte plat_len, byte numtracks)
+{
+	TileIndexDiff diff = cur_tile - north_tile;
+	Slope slope = GetTileSlope(cur_tile, NULL);
+
+	ResolverObject object;
+	NewStationResolver(&object, statspec, NULL, cur_tile);
+
+	object.callback        = CBID_STATION_LAND_SLOPE_CHECK;
+	object.callback_param1 = slope << 4 | slope ^ (axis == AXIS_Y && HasBit(slope, CORNER_W) != HasBit(slope, CORNER_E) ? SLOPE_EW : 0);
+	object.callback_param2 = numtracks << 24 | plat_len << 16 | (axis == AXIS_Y ? TileX(diff) << 8 | TileY(diff) : TileY(diff) << 8 | TileX(diff));
+	object.u.station.axis  = axis;
+
+	const SpriteGroup *group = ResolveStation(&object);
+	uint16 cb_res = group != NULL ? group->GetCallbackResult() : CALLBACK_FAILED;
+
+	/* Failed callback means success. */
+	if (cb_res == CALLBACK_FAILED) return CommandCost();
+
+	/* The meaning of bit 10 is inverted in the result of this callback. */
+	return GetErrorMessageFromLocationCallbackResult(ToggleBit(cb_res, 10), statspec->grf_prop.grffile->grfid, STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
+}
+
 
 /**
  * Allocate a StationSpec to a Station. This is called once per build operation.

--- a/src/newgrf_station.h
+++ b/src/newgrf_station.h
@@ -114,6 +114,7 @@
 SpriteID GetCustomStationRelocation(const StationSpec *statspec, BaseStation *st, TileIndex tile, uint32 var10 = 0);
 SpriteID GetCustomStationFoundationRelocation(const StationSpec *statspec, BaseStation *st, TileIndex tile, uint layout, uint edge_info);
 uint16 GetStationCallback(CallbackID callback, uint32 param1, uint32 param2, const StationSpec *statspec, BaseStation *st, TileIndex tile);
+CommandCost PerformStationTileSlopeCheck(TileIndex north_tile, TileIndex cur_tile, const StationSpec *statspec, Axis axis, byte plat_len, byte numtracks);
 
 /* Allocate a StationSpec to a Station. This is called once per build operation. */
 int AllocateSpecToStation(const StationSpec *statspec, BaseStation *st, bool exec);

--- a/src/station_cmd.cpp
+++ b/src/station_cmd.cpp
@@ -749,22 +749,36 @@
  * Checks if a rail station can be built at the given area.
  * @param tile_area Area to check.
  * @param flags Operation to perform.
- * @param invalid_dirs Prohibited directions (set of #DiagDirection).
+ * @param axis Rail station axis.
  * @param station StationID to be queried and returned if available.
  * @param rt The rail type to check for (overbuilding rail stations over rail).
  * @param affected_vehicles List of trains with PBS reservations on the tiles
+ * @param spec_class Station class.
+ * @param spec_index Index into the station class.
+ * @param plat_len Platform length.
+ * @param numtracks Number of platforms.
  * @return The cost in case of success, or an error code if it failed.
  */
-static CommandCost CheckFlatLandRailStation(TileArea tile_area, DoCommandFlag flags, uint invalid_dirs, StationID *station, RailType rt, SmallVector<Train *, 4> &affected_vehicles)
+static CommandCost CheckFlatLandRailStation(TileArea tile_area, DoCommandFlag flags, Axis axis, StationID *station, RailType rt, SmallVector<Train *, 4> &affected_vehicles, StationClassID spec_class, byte spec_index, byte plat_len, byte numtracks)
 {
 	CommandCost cost(EXPENSES_CONSTRUCTION);
 	int allowed_z = -1;
+	uint invalid_dirs = 5 << axis;
+
+	const StationSpec *statspec = StationClass::Get(spec_class, spec_index);
+	bool slope_cb = statspec != NULL && HasBit(statspec->callback_mask, CBM_STATION_SLOPE_CHECK);
 
 	TILE_AREA_LOOP(tile_cur, tile_area) {
 		CommandCost ret = CheckBuildableTile(tile_cur, invalid_dirs, allowed_z);
 		if (ret.Failed()) return ret;
 		cost.AddCost(ret);
 
+		if (slope_cb) {
+			/* Do slope check if requested. */
+			ret = PerformStationTileSlopeCheck(tile_area.tile, tile_cur, statspec, axis, plat_len, numtracks);
+			if (ret.Failed()) return ret;
+		}
+
 		/* if station is set, then we have special handling to allow building on top of already existing stations.
 		 * so station points to INVALID_STATION if we can build on any station.
 		 * Or it points to a station if we're only allowed to build on exactly that station. */
@@ -1140,7 +1154,7 @@
 	StationID est = INVALID_STATION;
 	SmallVector<Train *, 4> affected_vehicles;
 	/* Clear the land below the station. */
-	CommandCost cost = CheckFlatLandRailStation(TileArea(tile_org, w_org, h_org), flags, 5 << axis, &est, rt, affected_vehicles);
+	CommandCost cost = CheckFlatLandRailStation(TileArea(tile_org, w_org, h_org), flags, axis, &est, rt, affected_vehicles, spec_class, spec_index, plat_len, numtracks);
 	if (cost.Failed()) return cost;
 	/* Add construction expenses. */
 	cost.AddCost((numtracks * _price[PR_BUILD_STATION_RAIL] + _price[PR_BUILD_STATION_RAIL_LENGTH]) * plat_len);