diff --git a/lib/rules/template-no-invalid-aria-attributes.js b/lib/rules/template-no-invalid-aria-attributes.js
index 4a5c7a2a48..302c8267a7 100644
--- a/lib/rules/template-no-invalid-aria-attributes.js
+++ b/lib/rules/template-no-invalid-aria-attributes.js
@@ -11,16 +11,7 @@ function isNumeric(value) {
   return !Number.isNaN(Number(value));
 }
 
-function isValidAriaValue(attrName, value) {
-  const attrDef = aria.get(attrName);
-  if (!attrDef) {
-    return true;
-  }
-
-  if (value === 'undefined') {
-    return Boolean(attrDef.allowundefined);
-  }
-
+function validateByType(attrDef, value) {
   switch (attrDef.type) {
     case 'boolean': {
       return isBoolean(value);
@@ -60,6 +51,32 @@ function isValidAriaValue(attrName, value) {
   }
 }
 
+function isValidAriaValue(attrName, value) {
+  const attrDef = aria.get(attrName);
+  if (!attrDef) {
+    return true;
+  }
+
+  // Check whether 'undefined' is an explicit token in the attribute's value list
+  // (e.g. aria-orientation allows 'undefined' per aria-query) BEFORE applying the
+  // generic allowundefined shortcut. Otherwise valid tokens get rejected for
+  // attributes where allowundefined is false.
+  if (
+    value === 'undefined' &&
+    (attrDef.type === 'token' || attrDef.type === 'tokenlist') &&
+    Array.isArray(attrDef.values) &&
+    attrDef.values.includes('undefined')
+  ) {
+    return true;
+  }
+
+  if (value === 'undefined') {
+    return Boolean(attrDef.allowundefined);
+  }
+
+  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..aefa9d0cd9 100644
--- a/tests/lib/rules/template-no-invalid-aria-attributes.js
+++ b/tests/lib/rules/template-no-invalid-aria-attributes.js
@@ -32,6 +32,8 @@ ruleTester.run('template-no-invalid-aria-attributes', rule, {
     '<template><button type="submit" aria-disabled={{this.isDisabled}}>Submit</button></template>',
     '<template><div role="textbox" aria-sort={{if this.hasCustomSort "other" "ascending"}}></div></template>',
     '<template><div role="combobox" aria-expanded="undefined"></div></template>',
+    '<template><div role="slider" aria-orientation="undefined"></div></template>',
+    '<template><div role="slider" aria-orientation="horizontal"></div></template>',
     '<template><button aria-label={{if @isNew (t "actions.add") (t "actions.edit")}}></button></template>',
   ],
   invalid: [
@@ -121,6 +123,11 @@ 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' }],
+    },
   ],
 });
 
@@ -150,6 +157,8 @@ hbsRuleTester.run('template-no-invalid-aria-attributes', rule, {
     '<button type="submit" aria-disabled={{this.isDisabled}}>Submit</button>',
     '<div role="textbox" aria-sort={{if this.hasCustomSort "other" "ascending"}}></div>',
     '<div role="combobox" aria-expanded="undefined"></div>',
+    '<div role="slider" aria-orientation="undefined"></div>',
+    '<div role="slider" aria-orientation="horizontal"></div>',
     '<button aria-label={{if @isNew (t "actions.add") (t "actions.edit")}}></button>',
   ],
   invalid: [
@@ -223,5 +232,10 @@ 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' }],
+    },
   ],
 });