diff --git a/includes/ParamValidator/TypeDef/UserDef.php b/includes/ParamValidator/TypeDef/UserDef.php
index 0be2b3d46cf..772510d3461 100644
--- a/includes/ParamValidator/TypeDef/UserDef.php
+++ b/includes/ParamValidator/TypeDef/UserDef.php
@@ -8,7 +8,6 @@ use MediaWiki\User\UserIdentity;
 use MediaWiki\User\UserIdentityLookup;
 use MediaWiki\User\UserIdentityValue;
 use MediaWiki\User\UserNameUtils;
-use RequestContext;
 use TitleParser;
 use Wikimedia\IPUtils;
 use Wikimedia\Message\MessageValue;
@@ -164,26 +163,19 @@ class UserDef extends TypeDef {
 	private function processUser( string $value ): array {
 		// A user ID?
 		if ( preg_match( '/^#(\d+)$/D', $value, $m ) ) {
-			// We match the behavior of trying to create a User object
-			// based on the id. The name is:
-			// * the IP address of the current request, if the id is 0
-			// * the name of the relevant user in the database, if one exists
-			// * the name 'Unknown user' if it does not exist
+			// This used to use the IP address of the current request if the
+			// id was 0, to match the behavior of User objects, but was switched
+			// to "Unknown user" because the former behavior is likely unexpected.
+			// If the id corresponds to a user in the database, use that user, otherwise
+			// return a UserIdentityValue with id 0 (regardless of the input id) and
+			// the name "Unknown user"
 			$userId = (int)$m[1];
-			if ( $userId === 0 ) {
-				// TODO we probably shouldn't be falling back to the request IP,
-				// but if we really want to we shouldn't be doing it by accessing
-				// the global state like this
-				$currentIP = RequestContext::getMain()->getRequest()->getIP();
-				return [
-					'id',
-					new UserIdentityValue( 0, IPUtils::sanitizeIP( $currentIP ) )
-				];
-			}
-			// Check the database.
-			$userIdentity = $this->userIdentityLookup->getUserIdentityByUserId( $userId );
-			if ( $userIdentity ) {
-				return [ 'id', $userIdentity ];
+			if ( $userId !== 0 ) {
+				// Check the database.
+				$userIdentity = $this->userIdentityLookup->getUserIdentityByUserId( $userId );
+				if ( $userIdentity ) {
+					return [ 'id', $userIdentity ];
+				}
 			}
 			// Fall back to "Unknown user"
 			return [
diff --git a/tests/phpunit/includes/ParamValidator/TypeDef/UserDefTest.php b/tests/phpunit/includes/ParamValidator/TypeDef/UserDefTest.php
index 102b33190cc..ba7ca63a4b8 100644
--- a/tests/phpunit/includes/ParamValidator/TypeDef/UserDefTest.php
+++ b/tests/phpunit/includes/ParamValidator/TypeDef/UserDefTest.php
@@ -7,8 +7,6 @@ use MediaWiki\MediaWikiServices;
 use MediaWiki\User\UserIdentity;
 use MediaWiki\User\UserIdentityLookup;
 use MediaWiki\User\UserIdentityValue;
-use RequestContext;
-use WebRequest;
 use Wikimedia\Message\DataMessageValue;
 use Wikimedia\ParamValidator\ParamValidator;
 use Wikimedia\ParamValidator\SimpleCallbacks;
@@ -413,35 +411,12 @@ class UserDefTest extends TypeDefTestCase {
 		$this->assertSame( $expectName, $actual->getName() );
 	}
 
-	public function testProcessUser_id0() {
-		// User created by id, when that id is 0, falls back to context ip
-		// Use try-finally so that we don't interfere with other tests
-		$oldRequest = RequestContext::getMain()->getRequest();
-		try {
-			$mockRequest = $this->createMock( WebRequest::class );
-			$mockRequest->method( 'getIP' )->willReturn( '200.1.2.3' );
-			RequestContext::getMain()->setRequest( $mockRequest );
-			$userDef = $this->getInstance( new SimpleCallbacks( [] ), [] );
-			$res = $userDef->validate(
-				'', // $name, unused here
-				'#0',
-				[
-					UserDef::PARAM_ALLOWED_USER_TYPES => [ 'id' ],
-					UserDef::PARAM_RETURN_OBJECT => true,
-				], // $settings
-				[] // $options, unused here
-			);
-			$this->assertUserIdentity( $res, 0, '200.1.2.3' );
-		} finally {
-			RequestContext::getMain()->setRequest( $oldRequest );
-		}
-	}
-
-	public function testProcessUser_missingId() {
+	/**
+	 * @dataProvider provideMissingId
+	 */
+	public function testProcessUser_missingId( $missingId ) {
 		// User created by id, does not exist, falls back to "Unknown user"
 		// See our mock UserIdentityLookup for which ids and names exist
-		$missingId = 6;
-
 		$userDef = $this->getInstance( new SimpleCallbacks( [] ), [] );
 		$res = $userDef->validate(
 			'', // $name, unused here
@@ -457,6 +432,11 @@ class UserDefTest extends TypeDefTestCase {
 		$this->assertUserIdentity( $res, 0, "Unknown user" );
 	}
 
+	public function provideMissingId() {
+		yield "0 no longer matches request ip" => [ 0 ];
+		yield "Id with no user" => [ 6 ];
+	}
+
 	public function testProcessUser_validId() {
 		// User created by id, does exist
 		// See our mock UserIdentityLookup for which ids and names exist