diff --git a/rules/no-useless-undefined.js b/rules/no-useless-undefined.js
index 2c2497758e..6ee252a17b 100644
--- a/rules/no-useless-undefined.js
+++ b/rules/no-useless-undefined.js
@@ -1,7 +1,7 @@
 'use strict';
 const {isCommaToken} = require('@eslint-community/eslint-utils');
 const {replaceNodeOrTokenAndSpacesBefore} = require('./fix/index.js');
-const {isUndefined} = require('./ast/index.js');
+const {isUndefined, isFunction} = require('./ast/index.js');
 
 const messageId = 'no-useless-undefined';
 const messages = {
@@ -80,6 +80,9 @@ const isFunctionBindCall = node =>
 	&& node.callee.property.type === 'Identifier'
 	&& node.callee.property.name === 'bind';
 
+const isTypeScriptFile = context =>
+	/\.(?:ts|mts|cts|tsx)$/i.test(context.getPhysicalFilename());
+
 /** @param {import('eslint').Rule.RuleContext} context */
 const create = context => {
 	const {sourceCode} = context;
@@ -179,7 +182,24 @@ const create = context => {
 		) {
 			return getProblem(
 				node,
-				fixer => fixer.removeRange([node.parent.left.range[1], node.range[1]]),
+				function * (fixer) {
+					const assignmentPattern = node.parent;
+					const {left} = assignmentPattern;
+
+					yield fixer.removeRange([left.range[1], node.range[1]]);
+					if (
+						(left.typeAnnotation || isTypeScriptFile(context))
+						&& !left.optional
+						&& isFunction(assignmentPattern.parent)
+						&& assignmentPattern.parent.params.includes(assignmentPattern)
+					) {
+						yield (
+							left.typeAnnotation
+								? fixer.insertTextBefore(left.typeAnnotation, '?')
+								: fixer.insertTextAfter(left, '?')
+						);
+					}
+				},
 				/* CheckFunctionReturnType */ true,
 			);
 		}
diff --git a/test/no-useless-undefined.mjs b/test/no-useless-undefined.mjs
index 0901e83230..9964a7a14c 100644
--- a/test/no-useless-undefined.mjs
+++ b/test/no-useless-undefined.mjs
@@ -471,3 +471,34 @@ test.snapshot({
 		`,
 	],
 });
+
+test.snapshot({
+	testerOptions: {
+		parser: parsers.typescript,
+	},
+	valid: [],
+	invalid: [
+		'function f(foo: Type = undefined) {}',
+		'function f(foo?: Type = undefined) {}',
+		'const f = function(foo: Type = undefined) {}',
+		'const f = (foo: Type = undefined) => {}',
+		'const f = {method(foo: Type = undefined){}}',
+		'const f = class {method(foo: Type = undefined){}}',
+		'function f(foo = undefined) {}',
+		...[
+			undefined,
+			'foo.js',
+			'foo.ts',
+			'foo.MTs',
+			'foo.cts',
+			'foo.tsx',
+		].map(filename => ({
+			code: 'function f(foo = undefined) {}',
+			filename,
+		})),
+		{
+			code: 'function a({foo} = undefined) {}',
+			filename: 'foo.ts',
+		},
+	],
+});
diff --git a/test/snapshots/no-useless-undefined.mjs.md b/test/snapshots/no-useless-undefined.mjs.md
index 158c538dc4..8d4be87aa1 100644
--- a/test/snapshots/no-useless-undefined.mjs.md
+++ b/test/snapshots/no-useless-undefined.mjs.md
@@ -324,3 +324,263 @@ Generated by [AVA](https://avajs.dev).
         |                      ^^^^^^^^^ Do not use useless \`undefined\`.␊
       4 | </script>␊
     `
+
+## Invalid #1
+      1 | function f(foo: Type = undefined) {}
+
+> Output
+
+    `␊
+      1 | function f(foo?: Type) {}␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | function f(foo: Type = undefined) {}␊
+        |                        ^^^^^^^^^ Do not use useless \`undefined\`.␊
+    `
+
+## Invalid #2
+      1 | function f(foo?: Type = undefined) {}
+
+> Output
+
+    `␊
+      1 | function f(foo?: Type) {}␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | function f(foo?: Type = undefined) {}␊
+        |                         ^^^^^^^^^ Do not use useless \`undefined\`.␊
+    `
+
+## Invalid #3
+      1 | const f = function(foo: Type = undefined) {}
+
+> Output
+
+    `␊
+      1 | const f = function(foo?: Type) {}␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | const f = function(foo: Type = undefined) {}␊
+        |                                ^^^^^^^^^ Do not use useless \`undefined\`.␊
+    `
+
+## Invalid #4
+      1 | const f = (foo: Type = undefined) => {}
+
+> Output
+
+    `␊
+      1 | const f = (foo?: Type) => {}␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | const f = (foo: Type = undefined) => {}␊
+        |                        ^^^^^^^^^ Do not use useless \`undefined\`.␊
+    `
+
+## Invalid #5
+      1 | const f = {method(foo: Type = undefined){}}
+
+> Output
+
+    `␊
+      1 | const f = {method(foo?: Type){}}␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | const f = {method(foo: Type = undefined){}}␊
+        |                               ^^^^^^^^^ Do not use useless \`undefined\`.␊
+    `
+
+## Invalid #6
+      1 | const f = class {method(foo: Type = undefined){}}
+
+> Output
+
+    `␊
+      1 | const f = class {method(foo?: Type){}}␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | const f = class {method(foo: Type = undefined){}}␊
+        |                                     ^^^^^^^^^ Do not use useless \`undefined\`.␊
+    `
+
+## Invalid #7
+      1 | function f(foo = undefined) {}
+
+> Output
+
+    `␊
+      1 | function f(foo) {}␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | function f(foo = undefined) {}␊
+        |                  ^^^^^^^^^ Do not use useless \`undefined\`.␊
+    `
+
+## Invalid #8
+      1 | function f(foo = undefined) {}
+
+> Output
+
+    `␊
+      1 | function f(foo) {}␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | function f(foo = undefined) {}␊
+        |                  ^^^^^^^^^ Do not use useless \`undefined\`.␊
+    `
+
+## Invalid #9
+      1 | function f(foo = undefined) {}
+
+> Filename
+
+    `␊
+    foo.js␊
+    `
+
+> Output
+
+    `␊
+      1 | function f(foo) {}␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | function f(foo = undefined) {}␊
+        |                  ^^^^^^^^^ Do not use useless \`undefined\`.␊
+    `
+
+## Invalid #10
+      1 | function f(foo = undefined) {}
+
+> Filename
+
+    `␊
+    foo.ts␊
+    `
+
+> Output
+
+    `␊
+      1 | function f(foo?) {}␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | function f(foo = undefined) {}␊
+        |                  ^^^^^^^^^ Do not use useless \`undefined\`.␊
+    `
+
+## Invalid #11
+      1 | function f(foo = undefined) {}
+
+> Filename
+
+    `␊
+    foo.MTs␊
+    `
+
+> Output
+
+    `␊
+      1 | function f(foo?) {}␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | function f(foo = undefined) {}␊
+        |                  ^^^^^^^^^ Do not use useless \`undefined\`.␊
+    `
+
+## Invalid #12
+      1 | function f(foo = undefined) {}
+
+> Filename
+
+    `␊
+    foo.cts␊
+    `
+
+> Output
+
+    `␊
+      1 | function f(foo?) {}␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | function f(foo = undefined) {}␊
+        |                  ^^^^^^^^^ Do not use useless \`undefined\`.␊
+    `
+
+## Invalid #13
+      1 | function f(foo = undefined) {}
+
+> Filename
+
+    `␊
+    foo.tsx␊
+    `
+
+> Output
+
+    `␊
+      1 | function f(foo?) {}␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | function f(foo = undefined) {}␊
+        |                  ^^^^^^^^^ Do not use useless \`undefined\`.␊
+    `
+
+## Invalid #14
+      1 | function a({foo} = undefined) {}
+
+> Filename
+
+    `␊
+    foo.ts␊
+    `
+
+> Output
+
+    `␊
+      1 | function a({foo}?) {}␊
+    `
+
+> Error 1/1
+
+    `␊
+    > 1 | function a({foo} = undefined) {}␊
+        |                    ^^^^^^^^^ Do not use useless \`undefined\`.␊
+    `
diff --git a/test/snapshots/no-useless-undefined.mjs.snap b/test/snapshots/no-useless-undefined.mjs.snap
index df70b8a758..c393334e76 100644
Binary files a/test/snapshots/no-useless-undefined.mjs.snap and b/test/snapshots/no-useless-undefined.mjs.snap differ