diff --git tests/all_tests.nut tests/all_tests.nut
index 56387a680..189d19588 100644
--- tests/all_tests.nut
+++ tests/all_tests.nut
@@ -229,6 +229,7 @@ all_tests <- [
 	test_way_tram_has_double_slopes,
 	test_way_tunnel_build_straight,
 	test_way_tunnel_build_up_down,
+	test_way_tunnel_build_above_tunnel_slope,
 	test_way_tunnel_make_public,
 	test_wayobj_build_straight,
 	test_wayobj_build_disconnected,
diff --git tests/tests/test_way_tunnel.nut tests/tests/test_way_tunnel.nut
index 816b148fc..63a36ef91 100644
--- tests/tests/test_way_tunnel.nut
+++ tests/tests/test_way_tunnel.nut
@@ -396,6 +396,64 @@ function test_way_tunnel_build_up_down()
 }
 
 
+function test_way_tunnel_build_above_tunnel_slope()
+{
+	// Tests building on the tile above the top of a tunnel slope in pak64
+	// Should be allowed but, as of r11373, isn't.
+	// If way_height_clearance is >= 2, this test DOES NOT APPLY.
+	// FIXME: ignore this test if way_height_clearance >= 2 ?
+	local pl = player_x(0)
+	local default_tunnel = tunnel_desc_x.get_available_tunnels(wt_road)[0]
+	local digger = command_x(tool_build_tunnel)
+	local remover = command_x(tool_remover)
+	local setslope = command_x.set_slope
+
+	// Prepare area
+	ASSERT_EQUAL(command_x.grid_raise(pl, coord3d(1, 1, 1)), null)
+	ASSERT_EQUAL(command_x.grid_raise(pl, coord3d(2, 1, 1)), null)
+	ASSERT_EQUAL(command_x.grid_raise(pl, coord3d(1, 2, 1)), null)
+	ASSERT_EQUAL(command_x.grid_raise(pl, coord3d(2, 2, 1)), null)
+	ASSERT_EQUAL(command_x.grid_raise(pl, coord3d(1, 3, 1)), null)
+	ASSERT_EQUAL(command_x.grid_raise(pl, coord3d(2, 3, 1)), null)
+
+	{
+		digger.set_flags(2)
+		ASSERT_EQUAL(digger.work(pl, tile_x(1, 0, 0), default_tunnel.get_name()), null)
+		ASSERT_EQUAL(digger.work(pl, tile_x(1, 3, 0), default_tunnel.get_name()), null)
+		digger.set_flags(0)
+
+		ASSERT_EQUAL(digger.work(pl, tile_x(1, 0, 0), tile_x(1, 1, 0), default_tunnel.get_name()), null)
+		ASSERT_EQUAL(setslope(pl, coord3d(1, 1, 0), slope.all_down_slope), null)
+		ASSERT_EQUAL(setslope(pl, coord3d(1, 1, -1), slope.all_down_slope), null)
+		ASSERT_EQUAL(digger.work(pl, tile_x(1, 1, -2), tile_x(1, 2, -2), default_tunnel.get_name()), null)
+		ASSERT_EQUAL(setslope(pl, coord3d(1, 2, -2), slope.all_up_slope), null)
+
+		// Now for the real test: build at z=0 above simple slope from z=-2 to z=-1, should be allowed
+		ASSERT_EQUAL(digger.work(pl, tile_x(1, 3, 0), tile_x(1, 2, 0), default_tunnel.get_name()), null)
+		ASSERT_EQUAL(remover.work(pl, coord3d(1, 2, 0)), null)
+
+		ASSERT_EQUAL(setslope(pl, coord3d(1, 2, -1), slope.all_up_slope), null)
+		ASSERT_EQUAL(remover.work(pl, coord3d(1, 1, -2)), null)
+
+		// Now ensure we cannot overbuild a double slope from z=-2 to z=0
+		ASSERT_EQUAL(digger.work(pl, tile_x(1, 0, 0), tile_x(1, 2, 0), default_tunnel.get_name()), "")
+	}
+
+	// Clean up
+	ASSERT_EQUAL(remover.work(pl, coord3d(1, 2, -2)), null)
+	ASSERT_EQUAL(remover.work(pl, coord3d(1, 0, 0)), null)
+	ASSERT_EQUAL(remover.work(pl, coord3d(1, 3, 0)), null)
+	ASSERT_EQUAL(command_x.grid_lower(pl, coord3d(1, 1, 1)), null)
+	ASSERT_EQUAL(command_x.grid_lower(pl, coord3d(2, 1, 1)), null)
+	ASSERT_EQUAL(command_x.grid_lower(pl, coord3d(1, 2, 1)), null)
+	ASSERT_EQUAL(command_x.grid_lower(pl, coord3d(2, 2, 1)), null)
+	ASSERT_EQUAL(command_x.grid_lower(pl, coord3d(1, 3, 1)), null)
+	ASSERT_EQUAL(command_x.grid_lower(pl, coord3d(2, 3, 1)), null)
+
+	RESET_ALL_PLAYER_FUNDS()
+}
+
+
 function test_way_tunnel_make_public()
 {
 	local pl = player_x(0)