diff --git a/eval-config.nix b/eval-config.nix
index c30d88c7..cc0772de 100644
--- a/eval-config.nix
+++ b/eval-config.nix
@@ -46,6 +46,11 @@ let
     # Added in nixpkgs #136909, adds forward compatibility until 22.03 is deprecated.
     literalExpression = super.literalExpression or super.literalExample;
     literalDocBook = super.literalDocBook or super.literalExample;
+
+    # Removed in nixpkgs #237557, readded to faciliate Markdown transition.
+    mdDoc = text:
+      if ! self.isString text then throw "mdDoc expects a string."
+      else { _type = "mdDoc"; inherit text; };
   });
 
   eval = libExtended.evalModules (builtins.removeAttrs args [ "lib" "inputs" "pkgs" "system" ] // {