diff --git a/map.h b/map.h
index dab709e3fe..05f758f6dc 100644
--- a/map.h
+++ b/map.h
@@ -119,9 +119,11 @@ static inline TileIndexDiff ToTileIndexDiff(TileIndexDiffC tidc)
 
 uint TileAddWrap(TileIndex tile, int addx, int addy);
 
-static inline TileIndexDiffC TileIndexDiffCByDir(uint dir) {
-	extern const TileIndexDiffC _tileoffs_by_dir[4];
-	return _tileoffs_by_dir[dir];
+static inline TileIndexDiffC TileIndexDiffCByDiagDir(uint dir) {
+	extern const TileIndexDiffC _tileoffs_by_diagdir[4];
+
+	assert(dir < lengthof(_tileoffs_by_diagdir));
+	return _tileoffs_by_diagdir[dir];
 }
 
 /* Returns tile + the diff given in diff. If the result tile would end up
@@ -157,8 +159,7 @@ uint DistanceFromEdge(TileIndex); // shortest distance from any edge of the map
 		} while (var += TileDiffXY(0, 1) - (w), --h_cur != 0); \
 	}
 
-typedef enum DiagDirection DiagDirection;
-static inline TileIndexDiff TileOffsByDiagDir(DiagDirection dir)
+static inline TileIndexDiff TileOffsByDiagDir(uint dir)
 {
 	extern const TileIndexDiffC _tileoffs_by_diagdir[4];
 
@@ -166,8 +167,7 @@ static inline TileIndexDiff TileOffsByDiagDir(DiagDirection dir)
 	return ToTileIndexDiff(_tileoffs_by_diagdir[dir]);
 }
 
-typedef enum Direction Direction;
-static inline TileIndexDiff TileOffsByDir(Direction dir)
+static inline TileIndexDiff TileOffsByDir(uint dir)
 {
 	extern const TileIndexDiffC _tileoffs_by_dir[8];
 
diff --git a/npf.c b/npf.c
index 6a32cb387b..7e680e30a0 100644
--- a/npf.c
+++ b/npf.c
@@ -563,16 +563,16 @@ static void NPFFollowTrack(AyStar* aystar, OpenListNode* current)
 				 * outside of the depot. But, because the code layout is cleaner this
 				 * way, we will just pretend we are reversed already */
 				src_trackdir = ReverseTrackdir(src_trackdir);
-				dst_tile = AddTileIndexDiffCWrap(src_tile, TileIndexDiffCByDir(exitdir));
+				dst_tile = AddTileIndexDiffCWrap(src_tile, TileIndexDiffCByDiagDir(exitdir));
 			} else {
 				dst_tile = INVALID_TILE; /* Road vehicle heading inwards: dead end */
 			}
 		} else {
-			dst_tile = AddTileIndexDiffCWrap(src_tile, TileIndexDiffCByDir(exitdir));
+			dst_tile = AddTileIndexDiffCWrap(src_tile, TileIndexDiffCByDiagDir(exitdir));
 		}
 	} else {
 		/* This a normal tile, a bridge, a tunnel exit, etc. */
-		dst_tile = AddTileIndexDiffCWrap(src_tile, TileIndexDiffCByDir(TrackdirToExitdir(src_trackdir)));
+		dst_tile = AddTileIndexDiffCWrap(src_tile, TileIndexDiffCByDiagDir(TrackdirToExitdir(src_trackdir)));
 	}
 	if (dst_tile == INVALID_TILE) {
 		/* We reached the border of the map */
diff --git a/yapf/unittest/test_yapf.h b/yapf/unittest/test_yapf.h
index 952040faaa..685e6fcf79 100644
--- a/yapf/unittest/test_yapf.h
+++ b/yapf/unittest/test_yapf.h
@@ -169,7 +169,7 @@ struct CYapfTestBaseT
 		int z_org = Map::MapZ(x_org, y_org);
 		DiagDirection exitdir = TrackdirToExitdir(org.m_key.m_td);
 
-		TileIndexDiffC diff = TileIndexDiffCByDir(exitdir);
+		TileIndexDiffC diff = TileIndexDiffCByDiagDir(exitdir);
 		int x_new = x_org + diff.x;
 		int y_new = y_org + diff.y;
 		int z_new = Map::MapZ(x_new, y_new);