diff --git a/src/terraform_cmd.cpp b/src/terraform_cmd.cpp
index 0b82c60efe..71a171c665 100644
--- a/src/terraform_cmd.cpp
+++ b/src/terraform_cmd.cpp
@@ -270,7 +270,7 @@ CommandCost CmdTerraformLand(TileIndex tile, DoCommandFlag flags, uint32 p1, uin
 					}
 				}
 				/* Check if tunnel would take damage */
-				if (direction == -1 && IsTunnelInWay(tile, z_min, false)) {
+				if (direction == -1 && IsTunnelInWay(tile, z_min, true)) {
 					_terraform_err_tile = tile; // highlight the tile above the tunnel
 					return_cmd_error(STR_ERROR_EXCAVATION_WOULD_DAMAGE);
 				}
diff --git a/src/tunnel_map.cpp b/src/tunnel_map.cpp
index 358e83efc9..5ffb409c47 100644
--- a/src/tunnel_map.cpp
+++ b/src/tunnel_map.cpp
@@ -44,10 +44,10 @@ TileIndex GetOtherTunnelEnd(TileIndex tile)
  * Is there a tunnel in the way in any direction?
  * @param tile the tile to search from.
  * @param z the 'z' to search on.
- * @param not_allowed Only terra forming does not search between tunnel portals.
+ * @param chunnel_allowed True if chunnel mid-parts are allowed, used when terraforming.
  * @return true if and only if there is a tunnel.
  */
-bool IsTunnelInWay(TileIndex tile, int z, bool not_allowed)
+bool IsTunnelInWay(TileIndex tile, int z, bool chunnel_allowed)
 {
 	uint x = TileX(tile);
 	uint y = TileY(tile);
@@ -62,7 +62,7 @@ bool IsTunnelInWay(TileIndex tile, int z, bool not_allowed)
 			if (TileY(t->tile_n) != y || (int)TileHeight(t->tile_n) != z) continue; // dir DIAGDIR_SW
 		}
 
-		if (t->is_chunnel > not_allowed) {
+		if (t->is_chunnel && chunnel_allowed) {
 			/* Only if tunnel was build over water terraforming is allowed between portals. */
 			TileIndexDiff delta = GetTunnelBridgeDirection(t->tile_n) == DIAGDIR_SE ? TileOffsByDiagDir(DIAGDIR_SE) * 4 : 4;  // 4 tiles ramp.
 			if (tile < t->tile_n + delta || t->tile_s - delta < tile) return true;
diff --git a/src/tunnel_map.h b/src/tunnel_map.h
index 5d77822c6a..2ea126523f 100644
--- a/src/tunnel_map.h
+++ b/src/tunnel_map.h
@@ -51,7 +51,7 @@ static inline TunnelID GetTunnelIndex(TileIndex t)
 }
 
 TileIndex GetOtherTunnelEnd(TileIndex);
-bool IsTunnelInWay(TileIndex, int z, bool not_allowed = true);
+bool IsTunnelInWay(TileIndex, int z, bool chunnel_allowed = false);
 
 /**
  * Makes a road tunnel entrance
diff --git a/src/tunnelbridge_cmd.cpp b/src/tunnelbridge_cmd.cpp
index b06c20fe65..e0be7f26e1 100644
--- a/src/tunnelbridge_cmd.cpp
+++ b/src/tunnelbridge_cmd.cpp
@@ -740,7 +740,7 @@ CommandCost CmdBuildTunnel(TileIndex start_tile, DoCommandFlag flags, uint32 p1,
 			head_tiles = 0;
 			found_tunnel_tile = INVALID_TILE;
 		}
-		if (!_cheats.crossing_tunnels.value && IsTunnelInWay(end_tile, start_z, false)) {
+		if (!_cheats.crossing_tunnels.value && IsTunnelInWay(end_tile, start_z, true)) {
 			if (found_tunnel_tile == INVALID_TILE || is_chunnel) { // Remember the first or the last when we pass a tunnel.
 				found_tunnel_tile = end_tile;
 				head_tiles = 0;