diff --git a/lib/tests/modules.sh b/lib/tests/modules.sh
index 505c1c5a5fe4..f2e6d3b452b5 100755
--- a/lib/tests/modules.sh
+++ b/lib/tests/modules.sh
@@ -200,12 +200,12 @@ checkConfigError '.*A definition for option .bad. is not of type .non-empty .lis
 
 # types.attrTag
 checkConfigOutput '^true$' config.okChecks ./types-attrTag.nix
-checkConfigError 'A definition for option .intStrings\.syntaxError. is not of type .attribute-tagged union' config.intStrings.syntaxError ./types-attrTag.nix
-checkConfigError 'A definition for option .intStrings\.syntaxError2. is not of type .attribute-tagged union' config.intStrings.syntaxError2 ./types-attrTag.nix
-checkConfigError 'A definition for option .intStrings\.syntaxError3. is not of type .attribute-tagged union' config.intStrings.syntaxError3 ./types-attrTag.nix
-checkConfigError 'A definition for option .intStrings\.syntaxError4. is not of type .attribute-tagged union' config.intStrings.syntaxError4 ./types-attrTag.nix
-checkConfigError 'A definition for option .intStrings\.mergeError. is not of type .attribute-tagged union' config.intStrings.mergeError ./types-attrTag.nix
-checkConfigError 'A definition for option .intStrings\.badTagError. is not of type .attribute-tagged union' config.intStrings.badTagError ./types-attrTag.nix
+checkConfigError 'A definition for option .intStrings\.syntaxError. is not of type .attribute-tagged union with choices: left, right' config.intStrings.syntaxError ./types-attrTag.nix
+checkConfigError 'A definition for option .intStrings\.syntaxError2. is not of type .attribute-tagged union with choices: left, right' config.intStrings.syntaxError2 ./types-attrTag.nix
+checkConfigError 'A definition for option .intStrings\.syntaxError3. is not of type .attribute-tagged union with choices: left, right' config.intStrings.syntaxError3 ./types-attrTag.nix
+checkConfigError 'A definition for option .intStrings\.syntaxError4. is not of type .attribute-tagged union with choices: left, right' config.intStrings.syntaxError4 ./types-attrTag.nix
+checkConfigError 'A definition for option .intStrings\.mergeError. is not of type .attribute-tagged union with choices: left, right' config.intStrings.mergeError ./types-attrTag.nix
+checkConfigError 'A definition for option .intStrings\.badTagError. is not of type .attribute-tagged union with choices: left, right' config.intStrings.badTagError ./types-attrTag.nix
 checkConfigError 'A definition for option .intStrings\.badTagTypeError\.left. is not of type .signed integer.' config.intStrings.badTagTypeError.left ./types-attrTag.nix
 checkConfigError 'A definition for option .nested\.right\.left. is not of type .signed integer.' config.nested.right.left ./types-attrTag.nix
 checkConfigError 'In attrTag, each tag value must be an option, but tag int was a bare type, not wrapped in mkOption.' config.opt.int ./types-attrTag-wrong-decl.nix
diff --git a/lib/types.nix b/lib/types.nix
index e57ceafcbaa4..bc6e28ed9363 100644
--- a/lib/types.nix
+++ b/lib/types.nix
@@ -965,7 +965,7 @@ let
         in
         mkOptionType {
           name = "attrTag";
-          description = "attribute-tagged union";
+          description = "attribute-tagged union with choices: ${choicesStr}";
           descriptionClass = "noun";
           getSubOptions =
             prefix: mapAttrs (tagName: tagOption: tagOption // { loc = prefix ++ [ tagName ]; }) tags;