diff --git a/lib/rules/template-no-invalid-aria-attributes.js b/lib/rules/template-no-invalid-aria-attributes.js
index 4a5c7a2a48..6eead8bf76 100644
--- a/lib/rules/template-no-invalid-aria-attributes.js
+++ b/lib/rules/template-no-invalid-aria-attributes.js
@@ -11,16 +11,22 @@ function isNumeric(value) {
   return !Number.isNaN(Number(value));
 }
 
-function isValidAriaValue(attrName, value) {
-  const attrDef = aria.get(attrName);
-  if (!attrDef) {
-    return true;
-  }
+// In aria-query 5.3.2, `allowundefined: true` is set only on the four
+// boolean-like ARIA state attributes — `aria-expanded`, `aria-hidden`,
+// `aria-grabbed`, `aria-selected` — whose WAI-ARIA 1.2 value tables list
+// the literal string `"undefined"` as a spec-valid value meaning "state
+// is not applicable" (e.g. https://www.w3.org/TR/wai-aria-1.2/#aria-expanded).
+// The flag is nominally type-agnostic, but in practice this function only
+// green-lights `"undefined"` for that boolean-like subset; no non-boolean
+// ARIA attribute in aria-query currently sets `allowundefined`.
+function allowsUndefinedLiteral(attrDef, value) {
+  return value === 'undefined' && Boolean(attrDef.allowundefined);
+}
 
-  if (value === 'undefined') {
-    return Boolean(attrDef.allowundefined);
+function validateByType(attrDef, value) {
+  if (allowsUndefinedLiteral(attrDef, value)) {
+    return true;
   }
-
   switch (attrDef.type) {
     case 'boolean': {
       return isBoolean(value);
@@ -45,7 +51,9 @@ function isValidAriaValue(attrName, value) {
       return isNumeric(value) && !isBoolean(value);
     }
     case 'token': {
-      // aria-query stores boolean values as actual booleans, convert for comparison
+      // aria-query stores boolean values as actual booleans; stringify for comparison.
+      // The string literal 'undefined' that appears in some values arrays (e.g.
+      // aria-orientation) passes through this check naturally — no special-casing.
       const permittedValues = attrDef.values.map((v) =>
         typeof v === 'boolean' ? v.toString() : v
       );
@@ -60,6 +68,14 @@ function isValidAriaValue(attrName, value) {
   }
 }
 
+function isValidAriaValue(attrName, value) {
+  const attrDef = aria.get(attrName);
+  if (!attrDef) {
+    return true;
+  }
+  return validateByType(attrDef, value);
+}
+
 function getExpectedTypeDescription(attrName) {
   const attrDef = aria.get(attrName);
   if (!attrDef) {
diff --git a/tests/lib/rules/template-no-invalid-aria-attributes.js b/tests/lib/rules/template-no-invalid-aria-attributes.js
index 7f8e10b8e6..163792bf3e 100644
--- a/tests/lib/rules/template-no-invalid-aria-attributes.js
+++ b/tests/lib/rules/template-no-invalid-aria-attributes.js
@@ -31,7 +31,24 @@ ruleTester.run('template-no-invalid-aria-attributes', rule, {
     '<template><CustomComponent @ariaRequired={{this.ariaRequired}} aria-errormessage="errorId" /></template>',
     '<template><button type="submit" aria-disabled={{this.isDisabled}}>Submit</button></template>',
     '<template><div role="textbox" aria-sort={{if this.hasCustomSort "other" "ascending"}}></div></template>',
+    // Boolean-type attributes with allowundefined: true per aria-query — the
+    // string "undefined" is spec-valid (WAI-ARIA 1.2 value tables for these
+    // attrs list true/false/undefined). All 4 share the same code path.
     '<template><div role="combobox" aria-expanded="undefined"></div></template>',
+    '<template><div aria-hidden="undefined"></div></template>',
+    '<template><div aria-grabbed="undefined" draggable="true"></div></template>',
+    '<template><div role="option" aria-selected="undefined"></div></template>',
+
+    // Token-type aria-orientation lists "undefined" in its values array;
+    // passes the natural token check (no special-casing needed).
+    '<template><div role="slider" aria-orientation="undefined"></div></template>',
+    '<template><div role="slider" aria-orientation="horizontal"></div></template>',
+
+    // aria-pressed is tristate WITHOUT allowundefined — string "undefined"
+    // is NOT accepted. Explicit valid values still work.
+    '<template><button aria-pressed="true">Toggle</button></template>',
+    '<template><button aria-pressed="false">Toggle</button></template>',
+    '<template><button aria-pressed="mixed">Toggle</button></template>',
     '<template><button aria-label={{if @isNew (t "actions.add") (t "actions.edit")}}></button></template>',
   ],
   invalid: [
@@ -121,6 +138,18 @@ ruleTester.run('template-no-invalid-aria-attributes', rule, {
       output: null,
       errors: [{ messageId: 'invalidAriaAttributeValue' }],
     },
+    {
+      code: '<template><div role="slider" aria-orientation="sideways"></div></template>',
+      output: null,
+      errors: [{ messageId: 'invalidAriaAttributeValue' }],
+    },
+    // aria-pressed is tristate WITHOUT allowundefined — string "undefined"
+    // is spec-invalid here (aria-query doesn't mark it allowundefined).
+    {
+      code: '<template><button aria-pressed="undefined">Toggle</button></template>',
+      output: null,
+      errors: [{ messageId: 'invalidAriaAttributeValue' }],
+    },
   ],
 });
 
@@ -149,7 +178,21 @@ hbsRuleTester.run('template-no-invalid-aria-attributes', rule, {
     '<CustomComponent @ariaRequired={{this.ariaRequired}} aria-errormessage="errorId" />',
     '<button type="submit" aria-disabled={{this.isDisabled}}>Submit</button>',
     '<div role="textbox" aria-sort={{if this.hasCustomSort "other" "ascending"}}></div>',
+    // Boolean-type attrs with allowundefined (spec-valid "undefined" literal):
     '<div role="combobox" aria-expanded="undefined"></div>',
+    '<div aria-hidden="undefined"></div>',
+    '<div aria-grabbed="undefined" draggable="true"></div>',
+    '<div role="option" aria-selected="undefined"></div>',
+
+    // Token-type aria-orientation — "undefined" passes via values list:
+    '<div role="slider" aria-orientation="undefined"></div>',
+    '<div role="slider" aria-orientation="horizontal"></div>',
+
+    // aria-pressed is tristate WITHOUT allowundefined; valid values:
+    '<button aria-pressed="true">Toggle</button>',
+    '<button aria-pressed="false">Toggle</button>',
+    '<button aria-pressed="mixed">Toggle</button>',
+
     '<button aria-label={{if @isNew (t "actions.add") (t "actions.edit")}}></button>',
   ],
   invalid: [
@@ -223,5 +266,16 @@ hbsRuleTester.run('template-no-invalid-aria-attributes', rule, {
       output: null,
       errors: [{ messageId: 'invalidAriaAttributeValue' }],
     },
+    {
+      code: '<div role="slider" aria-orientation="sideways"></div>',
+      output: null,
+      errors: [{ messageId: 'invalidAriaAttributeValue' }],
+    },
+    // aria-pressed has no allowundefined — "undefined" is spec-invalid here.
+    {
+      code: '<button aria-pressed="undefined">Toggle</button>',
+      output: null,
+      errors: [{ messageId: 'invalidAriaAttributeValue' }],
+    },
   ],
 });