diff --git a/changelog.md b/changelog.md
index 07fe4957731e..59eee5efeb8d 100644
--- a/changelog.md
+++ b/changelog.md
@@ -163,6 +163,8 @@
      (issue #3050).
    * Fixed a crash when using certain invalid color= values.
    * Fixed: unit halo remained after undoing a recall (issue #3065).
+   * [change_theme] no longer causes a Lua error when theme= is not specified
+     instead of explicitly set to an empty string.
 
 ## Version 1.13.12
  ### Security fixes
diff --git a/data/lua/wml-tags.lua b/data/lua/wml-tags.lua
index a0ed3a55a74f..28866ea1cf23 100644
--- a/data/lua/wml-tags.lua
+++ b/data/lua/wml-tags.lua
@@ -920,7 +920,13 @@ function wml_actions.reset_fog(cfg)
 end
 
 function wesnoth.wml_actions.change_theme(cfg)
-	wesnoth.game_config.theme = cfg.theme
+	local new_theme = cfg.theme
+
+	if new_theme == nil then
+		new_theme = ""
+	end
+
+	wesnoth.game_config.theme = new_theme
 end
 
 function wesnoth.wml_actions.zoom(cfg)