diff --git a/changelog.md b/changelog.md
index f995e9e9a31f..a1f96d8c23b9 100644
--- a/changelog.md
+++ b/changelog.md
@@ -3,6 +3,7 @@
    * Micro AIs
      * Add [avoid] tag functionality to Multipack Wolves, Wolves, Swarm and Goto Micro AIs
      * Support named locations for [micro_ai] tag location keys
+     * Goto and Assassin: fix MAIs not working with tunnels when using custom path finding cost functions
    * Experimental AI
      * Deprecate EXPERIMENTAL_AI macro: use ai_algorithm=experimental_ai in the [ai] tag instead
      * Convert to using external candidate actions
diff --git a/data/ai/micro_ais/cas/ca_assassin_move.lua b/data/ai/micro_ais/cas/ca_assassin_move.lua
index 9414299607d1..68eda8f35162 100644
--- a/data/ai/micro_ais/cas/ca_assassin_move.lua
+++ b/data/ai/micro_ais/cas/ca_assassin_move.lua
@@ -138,11 +138,11 @@ function ca_assassin_move:execution(cfg)
         end
     end
 
-    local path, cost = wesnoth.find_path(unit, target.x, target.y,
-        function(x, y, current_cost)
+    local path, cost = wesnoth.find_path(unit, target.x, target.y, {
+        calculate = function(x, y, current_cost)
             return custom_cost(x, y, unit, enemy_rating_map, prefer_map)
         end
-    )
+    })
 
     local path_map = LS.of_pairs(path)
 
diff --git a/data/ai/micro_ais/cas/ca_goto.lua b/data/ai/micro_ais/cas/ca_goto.lua
index c1425c855ca1..3de0d7004cb5 100644
--- a/data/ai/micro_ais/cas/ca_goto.lua
+++ b/data/ai/micro_ais/cas/ca_goto.lua
@@ -150,11 +150,11 @@ function ca_goto:execution(cfg, data)
             else  -- Otherwise find the best path to take
                 local path, cost
                 if GO_avoid_map or cfg.avoid_enemies then
-                    path, cost = wesnoth.find_path(unit, loc[1], loc[2],
-                        function(x, y, current_cost)
+                    path, cost = wesnoth.find_path(unit, loc[1], loc[2], {
+                        calculate = function(x, y, current_cost)
                             return custom_cost(x, y, unit, GO_avoid_map, enemy_map, enemy_attack_map, cfg.avoid_enemies)
                         end
-                    )
+                    })
                 else
                     local enemy_at_goal
                     if cfg.ignore_enemy_at_goal then