diff --git a/lib/rules/template-require-mandatory-role-attributes.js b/lib/rules/template-require-mandatory-role-attributes.js
index f399da3229..66153be724 100644
--- a/lib/rules/template-require-mandatory-role-attributes.js
+++ b/lib/rules/template-require-mandatory-role-attributes.js
@@ -1,46 +1,58 @@
 const { roles } = require('aria-query');
 
-function createRequiredAttributeErrorMessage(attrs, role) {
-  if (attrs.length < 2) {
-    return `The attribute ${attrs[0]} is required by the role ${role}`;
-  }
-
-  return `The attributes ${attrs.join(', ')} are required by the role ${role}`;
-}
-
-function getStaticRoleFromElement(node) {
+// ARIA role values are whitespace-separated tokens compared ASCII-case-insensitively.
+// Returns the list of normalised tokens, or undefined when the attribute is
+// missing or dynamic.
+function getStaticRolesFromElement(node) {
   const roleAttr = node.attributes?.find((attr) => attr.name === 'role');
 
   if (roleAttr?.value?.type === 'GlimmerTextNode') {
-    return roleAttr.value.chars || undefined;
+    return splitRoleTokens(roleAttr.value.chars);
   }
 
   return undefined;
 }
 
-function getStaticRoleFromMustache(node) {
+function getStaticRolesFromMustache(node) {
   const rolePair = node.hash?.pairs?.find((pair) => pair.key === 'role');
 
   if (rolePair?.value?.type === 'GlimmerStringLiteral') {
-    return rolePair.value.value;
+    return splitRoleTokens(rolePair.value.value);
   }
 
   return undefined;
 }
 
-function getMissingRequiredAttributes(role, foundAriaAttributes) {
-  const roleDefinition = roles.get(role);
-
-  if (!roleDefinition) {
-    return null;
+function splitRoleTokens(value) {
+  if (!value) {
+    return undefined;
   }
+  const tokens = value.trim().toLowerCase().split(/\s+/u).filter(Boolean);
+  return tokens.length > 0 ? tokens : undefined;
+}
 
-  const requiredAttributes = Object.keys(roleDefinition.requiredProps);
-  const missingRequiredAttributes = requiredAttributes.filter(
-    (requiredAttribute) => !foundAriaAttributes.includes(requiredAttribute)
-  );
-
-  return missingRequiredAttributes.length > 0 ? missingRequiredAttributes : null;
+// For an ARIA role-fallback list like "combobox listbox", check required
+// attributes against the FIRST recognised role (the primary) per ARIA 1.2
+// role-fallback semantics — a user agent picks the first role it recognises.
+// Diverges from jsx-a11y, which validates every recognised token.
+function getMissingRequiredAttributes(roleTokens, foundAriaAttributes) {
+  for (const role of roleTokens) {
+    const roleDefinition = roles.get(role);
+    if (!roleDefinition) {
+      continue;
+    }
+    const requiredAttributes = Object.keys(roleDefinition.requiredProps);
+    const missingRequiredAttributes = requiredAttributes
+      .filter((requiredAttribute) => !foundAriaAttributes.includes(requiredAttribute))
+      // Sort for deterministic report order (aria-query's requiredProps
+      // iteration order is not guaranteed stable across versions).
+      .sort();
+    return {
+      role,
+      missing: missingRequiredAttributes.length > 0 ? missingRequiredAttributes : null,
+    };
+  }
+  return null;
 }
 
 /** @type {import('eslint').Rule.RuleModule} */
@@ -83,9 +95,9 @@ module.exports = {
 
     return {
       GlimmerElementNode(node) {
-        const role = getStaticRoleFromElement(node);
+        const roleTokens = getStaticRolesFromElement(node);
 
-        if (!role) {
+        if (!roleTokens) {
           return;
         }
 
@@ -93,17 +105,17 @@ module.exports = {
           .filter((attribute) => attribute.name?.startsWith('aria-'))
           .map((attribute) => attribute.name);
 
-        const missingRequiredAttributes = getMissingRequiredAttributes(role, foundAriaAttributes);
+        const result = getMissingRequiredAttributes(roleTokens, foundAriaAttributes);
 
-        if (missingRequiredAttributes) {
-          reportMissingAttributes(node, role, missingRequiredAttributes);
+        if (result?.missing) {
+          reportMissingAttributes(node, result.role, result.missing);
         }
       },
 
       GlimmerMustacheStatement(node) {
-        const role = getStaticRoleFromMustache(node);
+        const roleTokens = getStaticRolesFromMustache(node);
 
-        if (!role) {
+        if (!roleTokens) {
           return;
         }
 
@@ -111,10 +123,10 @@ module.exports = {
           .filter((pair) => pair.key.startsWith('aria-'))
           .map((pair) => pair.key);
 
-        const missingRequiredAttributes = getMissingRequiredAttributes(role, foundAriaAttributes);
+        const result = getMissingRequiredAttributes(roleTokens, foundAriaAttributes);
 
-        if (missingRequiredAttributes) {
-          reportMissingAttributes(node, role, missingRequiredAttributes);
+        if (result?.missing) {
+          reportMissingAttributes(node, result.role, result.missing);
         }
       },
     };
diff --git a/tests/audit/role-has-required-aria/peer-parity.js b/tests/audit/role-has-required-aria/peer-parity.js
new file mode 100644
index 0000000000..98bd770056
--- /dev/null
+++ b/tests/audit/role-has-required-aria/peer-parity.js
@@ -0,0 +1,207 @@
+// Audit fixture — translates peer-plugin test cases into assertions against
+// our rule (`ember/template-require-mandatory-role-attributes`). Runs as
+// part of the default Vitest suite (via the `tests/**/*.js` include glob)
+// and serves double-duty: (1) auditable record of peer-parity divergences,
+// (2) regression coverage pinning CURRENT behavior. Each case encodes what
+// OUR rule does today; divergences from upstream plugins are annotated as
+// `DIVERGENCE —`. Peer-only constructs that can't be translated to Ember
+// templates (JSX spread props, Vue v-bind, Angular `$event`, undefined-handler
+// expression analysis) are marked `AUDIT-SKIP`.
+//
+// Source files (context/ checkouts):
+//   - eslint-plugin-jsx-a11y-main/src/rules/role-has-required-aria-props.js
+//   - eslint-plugin-jsx-a11y-main/__tests__/src/rules/role-has-required-aria-props-test.js
+//   - eslint-plugin-vuejs-accessibility-main/src/rules/role-has-required-aria-props.ts
+//   - angular-eslint-main/packages/eslint-plugin-template/src/rules/role-has-required-aria.ts
+//   - angular-eslint-main/packages/eslint-plugin-template/tests/rules/role-has-required-aria/cases.ts
+//   - eslint-plugin-lit-a11y/lib/rules/role-has-required-aria-attrs.js
+
+'use strict';
+
+const rule = require('../../../lib/rules/template-require-mandatory-role-attributes');
+const RuleTester = require('eslint').RuleTester;
+
+const ruleTester = new RuleTester({
+  parser: require.resolve('ember-eslint-parser'),
+  parserOptions: { ecmaVersion: 2022, sourceType: 'module' },
+});
+
+ruleTester.run('audit:role-has-required-aria (gts)', rule, {
+  valid: [
+    // === Upstream parity (valid everywhere) ===
+    '<template><div /></template>',
+    '<template><div role="button" /></template>', // no required props
+    '<template><div role="heading" aria-level="2" /></template>',
+    '<template><span role="button">X</span></template>',
+    // checkbox with aria-checked — valid in all plugins.
+    '<template><div role="checkbox" aria-checked="false" /></template>',
+    // combobox with BOTH required props (jsx-a11y, vue, ours).
+    '<template><div role="combobox" aria-expanded="false" aria-controls="id" /></template>',
+    // scrollbar requires aria-valuenow, aria-valuemin, aria-valuemax, aria-controls, aria-orientation.
+    // slider similarly — we leave the all-present case off for brevity.
+
+    // Dynamic role — skipped by all.
+    '<template><div role={{this.role}} /></template>',
+
+    // Unknown role — jsx-a11y filters out unknown, we return null. Both allow.
+    '<template><div role="foobar" /></template>',
+
+    // === DIVERGENCE — <input type="checkbox" role="switch"> ===
+    // jsx-a11y: VALID via `isSemanticRoleElement` (semantic input[type=checkbox]
+    //   counts as already-declaring aria-checked via its `checked` state).
+    // vue-a11y: VALID via explicit carve-out in filterRequiredPropsExceptions.
+    // angular: VALID via isSemanticRoleElement.
+    // Our rule: INVALID — we treat every element generically and `switch` has
+    //   `aria-checked` as a required prop. Captured in invalid section below.
+
+    // === Partial parity — space-separated role tokens ===
+    // jsx-a11y + vue: split on whitespace, validate EACH recognised token.
+    // Our rule: splits on whitespace, validates only the FIRST recognised
+    //   token (ARIA 1.2 §4.1 role-fallback semantics — UA picks the first
+    //   recognised role). So `<div role="button combobox">` — which has
+    //   "button" as the first recognised token (no required attrs) —
+    //   remains valid for us but jsx-a11y would flag it for missing
+    //   combobox attrs.
+    '<template><div role="button combobox" /></template>',
+    // Both-token case where the first token HAS no required attrs: valid
+    //   for us, invalid for jsx-a11y.
+    '<template><div role="heading button" aria-level="2" /></template>',
+  ],
+
+  invalid: [
+    // === Upstream parity (invalid everywhere) ===
+    {
+      code: '<template><div role="slider" /></template>',
+      output: null,
+      errors: [{ messageId: 'missingAttributes' }],
+    },
+    {
+      code: '<template><div role="checkbox" /></template>',
+      output: null,
+      errors: [{ messageId: 'missingAttributes' }],
+    },
+    {
+      code: '<template><div role="combobox" /></template>',
+      output: null,
+      errors: [{ messageId: 'missingAttributes' }],
+    },
+    {
+      code: '<template><div role="scrollbar" /></template>',
+      output: null,
+      errors: [{ messageId: 'missingAttributes' }],
+    },
+    {
+      code: '<template><div role="heading" /></template>',
+      output: null,
+      errors: [{ messageId: 'missingAttributes' }],
+    },
+    {
+      code: '<template><div role="option" /></template>',
+      output: null,
+      errors: [{ messageId: 'missingAttributes' }],
+    },
+
+    // === Partial parity — partial attrs present, still missing one ===
+    // jsx-a11y flags `<div role="scrollbar" aria-valuemax aria-valuemin />`
+    //   (missing aria-controls/aria-orientation/aria-valuenow).
+    // Our rule: also flags — missing-attrs list non-empty. Parity.
+    {
+      code: '<template><div role="combobox" aria-controls="x" /></template>',
+      output: null,
+      errors: [{ messageId: 'missingAttributes' }],
+    },
+
+    // === Parity — case-insensitive role comparison ===
+    // jsx-a11y + vue + angular lowercase the role value before lookup.
+    // Our rule now does the same, so `<div role="COMBOBOX" />` → INVALID
+    //   (missing aria-expanded / aria-controls).
+    {
+      code: '<template><div role="COMBOBOX" /></template>',
+      output: null,
+      errors: [{ messageId: 'missingAttributes' }],
+    },
+    {
+      code: '<template><div role="SLIDER" /></template>',
+      output: null,
+      errors: [{ messageId: 'missingAttributes' }],
+    },
+
+    // === Parity — whitespace-separated roles, first recognised validated ===
+    // `<div role="combobox listbox">` — both tokens are recognised roles
+    //   with required attrs. Per ARIA role-fallback semantics we validate
+    //   the first recognised token (combobox). jsx-a11y validates every
+    //   token; both plugins end up flagging this same code (though our
+    //   error names `combobox`, jsx-a11y may cite all missing attrs).
+    {
+      code: '<template><div role="combobox listbox" /></template>',
+      output: null,
+      errors: [{ messageId: 'missingAttributes' }],
+    },
+
+    // === DIVERGENCE — input[type=checkbox] role="switch" ===
+    // jsx-a11y / vue / angular: VALID (semantic exception).
+    // Our rule: INVALID (missing aria-checked). FALSE POSITIVE.
+    //   (This PR does not fix the semantic-input exception; separate
+    //   fix lives on fix/role-required-aria-checkbox-switch.)
+    {
+      code: '<template><input type="checkbox" role="switch" /></template>',
+      output: null,
+      errors: [{ messageId: 'missingAttributes' }],
+    },
+  ],
+});
+
+const hbsRuleTester = new RuleTester({
+  parser: require.resolve('ember-eslint-parser/hbs'),
+  parserOptions: { ecmaVersion: 2022, sourceType: 'module' },
+});
+
+hbsRuleTester.run('audit:role-has-required-aria (hbs)', rule, {
+  valid: [
+    '<div />',
+    '<div role="button" />',
+    '<div role="heading" aria-level="2" />',
+    '<div role="combobox" aria-expanded="false" aria-controls="id" />',
+    // Partial-parity: role-fallback validates only the first recognised
+    //   token. `<div role="button combobox">` is valid for us (first
+    //   recognised token "button" needs no attrs) but flagged by jsx-a11y.
+    '<div role="button combobox" />',
+    //   unknown role
+    '<div role="foobar" />',
+  ],
+  invalid: [
+    {
+      code: '<div role="slider" />',
+      output: null,
+      errors: [{ messageId: 'missingAttributes' }],
+    },
+    {
+      code: '<div role="checkbox" />',
+      output: null,
+      errors: [{ messageId: 'missingAttributes' }],
+    },
+    {
+      code: '<div role="heading" />',
+      output: null,
+      errors: [{ messageId: 'missingAttributes' }],
+    },
+    // Parity — case-insensitive comparison.
+    {
+      code: '<div role="COMBOBOX" />',
+      output: null,
+      errors: [{ messageId: 'missingAttributes' }],
+    },
+    // Parity — whitespace-separated roles, first recognised validated.
+    {
+      code: '<div role="combobox listbox" />',
+      output: null,
+      errors: [{ messageId: 'missingAttributes' }],
+    },
+    // DIVERGENCE: semantic input exception — jsx-a11y/vue/angular say VALID.
+    {
+      code: '<input type="checkbox" role="switch" />',
+      output: null,
+      errors: [{ messageId: 'missingAttributes' }],
+    },
+  ],
+});
diff --git a/tests/lib/rules/template-require-mandatory-role-attributes.js b/tests/lib/rules/template-require-mandatory-role-attributes.js
index 43af97d30a..c7198609dd 100644
--- a/tests/lib/rules/template-require-mandatory-role-attributes.js
+++ b/tests/lib/rules/template-require-mandatory-role-attributes.js
@@ -25,6 +25,11 @@ ruleTester.run('template-require-mandatory-role-attributes', rule, {
     '<template>{{foo-component role="button"}}</template>',
     '<template>{{foo-component role="unknown"}}</template>',
     '<template>{{foo-component role=role}}</template>',
+
+    // Case-insensitive role matching — ARIA role tokens compare as ASCII-case-insensitive.
+    '<template><div role="COMBOBOX" aria-expanded="false" aria-controls="ctrl" /></template>',
+    // Role fallback list — primary role's required attributes are satisfied.
+    '<template><div role="combobox listbox" aria-expanded="false" aria-controls="ctrl" /></template>',
   ],
 
   invalid: [
@@ -75,6 +80,27 @@ ruleTester.run('template-require-mandatory-role-attributes', rule, {
       output: null,
       errors: [{ message: 'The attribute aria-checked is required by the role checkbox' }],
     },
+
+    // Case-insensitive role matching — uppercase role missing required props is flagged.
+    {
+      code: '<template><div role="COMBOBOX"></div></template>',
+      output: null,
+      errors: [
+        {
+          message: 'The attributes aria-controls, aria-expanded are required by the role combobox',
+        },
+      ],
+    },
+    // Role-fallback list: when the primary role is missing required props, flag it.
+    {
+      code: '<template><div role="combobox listbox"></div></template>',
+      output: null,
+      errors: [
+        {
+          message: 'The attributes aria-controls, aria-expanded are required by the role combobox',
+        },
+      ],
+    },
   ],
 });
 
@@ -105,6 +131,11 @@ hbsRuleTester.run('template-require-mandatory-role-attributes', rule, {
     '{{foo-component role="button"}}',
     '{{foo-component role="unknown"}}',
     '{{foo-component role=role}}',
+
+    // Case-insensitive role matching — ARIA role tokens compare as ASCII-case-insensitive.
+    '<div role="COMBOBOX" aria-expanded="false" aria-controls="ctrl" />',
+    // Role fallback list — primary role's required attributes are satisfied.
+    '<div role="combobox listbox" aria-expanded="false" aria-controls="ctrl" />',
   ],
   invalid: [
     {
@@ -146,5 +177,26 @@ hbsRuleTester.run('template-require-mandatory-role-attributes', rule, {
       output: null,
       errors: [{ message: 'The attribute aria-checked is required by the role checkbox' }],
     },
+
+    // Case-insensitive role matching — uppercase role missing required props is flagged.
+    {
+      code: '<div role="COMBOBOX"></div>',
+      output: null,
+      errors: [
+        {
+          message: 'The attributes aria-controls, aria-expanded are required by the role combobox',
+        },
+      ],
+    },
+    // Role-fallback list: when the primary role is missing required props, flag it.
+    {
+      code: '<div role="combobox listbox"></div>',
+      output: null,
+      errors: [
+        {
+          message: 'The attributes aria-controls, aria-expanded are required by the role combobox',
+        },
+      ],
+    },
   ],
 });