diff --git a/src/clear_map.h b/src/clear_map.h
--- a/src/clear_map.h
+++ b/src/clear_map.h
@@ -126,7 +126,7 @@ static inline void MakeClear(TileIndex t
 {
 	/* If this is a non-bridgeable tile, clear the bridge bits while the rest
 	 * of the tile information is still here. */
-	if (!MayHaveBridgeAbove(t)) SB(_m[t].extra, 6, 2, 0);
+	if (!MayHaveBridgeAbove(t)) SB(_m[t].m6, 6, 2, 0);
 
 	SetTileType(t, MP_CLEAR);
 	SetTileOwner(t, OWNER_NONE);
@@ -134,7 +134,7 @@ static inline void MakeClear(TileIndex t
 	_m[t].m3 = 0;
 	_m[t].m4 = 0 << 5 | 0 << 2;
 	SetClearGroundDensity(t, g, density);
-	SB(_m[t].extra, 2, 4, 0);
+	SB(_m[t].m6, 2, 4, 0); ///< Clear the rest of m6, bits 2 to 5
 }