diff --git a/includes/user/User.php b/includes/user/User.php
index 3fcba4698d0..fa74cb341e3 100644
--- a/includes/user/User.php
+++ b/includes/user/User.php
@@ -28,6 +28,7 @@ use MediaWiki\Auth\AuthenticationResponse;
 use MediaWiki\Auth\AuthenticationRequest;
 use MediaWiki\User\UserIdentity;
 use MediaWiki\Logger\LoggerFactory;
+use Wikimedia\Assert\Assert;
 use Wikimedia\IPSet;
 use Wikimedia\ScopedCallback;
 use Wikimedia\Rdbms\Database;
@@ -1749,6 +1750,23 @@ class User implements IDBAccessObject, UserIdentity {
 		}
 	}
 
+	/** @var array|null */
+	private static $defOpt = null;
+	/** @var string|null */
+	private static $defOptLang = null;
+
+	/**
+	 * Reset the process cache of default user options. This is only necessary
+	 * if the wiki configuration has changed since defaults were calculated,
+	 * and as such should only be performed inside the testing suite that
+	 * regularly changes wiki configuration.
+	 */
+	public static function resetGetDefaultOptionsForTestsOnly() {
+		Assert::invariant( defined( 'MW_PHPUNIT_TEST' ), 'Unit tests only' );
+		self::$defOpt = null;
+		self::$defOptLang = null;
+	}
+
 	/**
 	 * Combine the language default options with any site-specific options
 	 * and add the default language variants.
@@ -1758,26 +1776,23 @@ class User implements IDBAccessObject, UserIdentity {
 	public static function getDefaultOptions() {
 		global $wgNamespacesToBeSearchedDefault, $wgDefaultUserOptions, $wgDefaultSkin;
 
-		static $defOpt = null;
-		static $defOptLang = null;
-
 		$contLang = MediaWikiServices::getInstance()->getContentLanguage();
-		if ( $defOpt !== null && $defOptLang === $contLang->getCode() ) {
+		if ( self::$defOpt !== null && self::$defOptLang === $contLang->getCode() ) {
 			// The content language does not change (and should not change) mid-request, but the
 			// unit tests change it anyway, and expect this method to return values relevant to the
 			// current content language.
-			return $defOpt;
+			return self::$defOpt;
 		}
 
-		$defOpt = $wgDefaultUserOptions;
+		self::$defOpt = $wgDefaultUserOptions;
 		// Default language setting
-		$defOptLang = $contLang->getCode();
-		$defOpt['language'] = $defOptLang;
+		self::$defOptLang = $contLang->getCode();
+		self::$defOpt['language'] = self::$defOptLang;
 		foreach ( LanguageConverter::$languagesWithVariants as $langCode ) {
 			if ( $langCode === $contLang->getCode() ) {
-				$defOpt['variant'] = $langCode;
+				self::$defOpt['variant'] = $langCode;
 			} else {
-				$defOpt["variant-$langCode"] = $langCode;
+				self::$defOpt["variant-$langCode"] = $langCode;
 			}
 		}
 
@@ -1785,13 +1800,13 @@ class User implements IDBAccessObject, UserIdentity {
 		// since extensions may change the set of searchable namespaces depending
 		// on user groups/permissions.
 		foreach ( $wgNamespacesToBeSearchedDefault as $nsnum => $val ) {
-			$defOpt['searchNs' . $nsnum] = (bool)$val;
+			self::$defOpt['searchNs' . $nsnum] = (bool)$val;
 		}
-		$defOpt['skin'] = Skin::normalizeKey( $wgDefaultSkin );
+		self::$defOpt['skin'] = Skin::normalizeKey( $wgDefaultSkin );
 
-		Hooks::run( 'UserGetDefaultOptions', [ &$defOpt ] );
+		Hooks::run( 'UserGetDefaultOptions', [ &self::$defOpt ] );
 
-		return $defOpt;
+		return self::$defOpt;
 	}
 
 	/**
diff --git a/tests/phpunit/MediaWikiTestCase.php b/tests/phpunit/MediaWikiTestCase.php
index 36d66fb2aa5..f43f0a9dd3f 100644
--- a/tests/phpunit/MediaWikiTestCase.php
+++ b/tests/phpunit/MediaWikiTestCase.php
@@ -361,6 +361,7 @@ abstract class MediaWikiTestCase extends PHPUnit\Framework\TestCase {
 	public static function resetNonServiceCaches() {
 		global $wgRequest, $wgJobClasses;
 
+		User::resetGetDefaultOptionsForTestsOnly();
 		foreach ( $wgJobClasses as $type => $class ) {
 			JobQueueGroup::singleton()->get( $type )->delete();
 		}
diff --git a/tests/phpunit/includes/specials/SpecialWatchlistTest.php b/tests/phpunit/includes/specials/SpecialWatchlistTest.php
index 28e26a082bb..642ae3e2de3 100644
--- a/tests/phpunit/includes/specials/SpecialWatchlistTest.php
+++ b/tests/phpunit/includes/specials/SpecialWatchlistTest.php
@@ -59,7 +59,44 @@ class SpecialWatchlistTest extends SpecialPageTestBase {
 	/**
 	 * @dataProvider provideFetchOptionsFromRequest
 	 */
-	public function testFetchOptionsFromRequest( $expectedValues, $preferences, $inputParams ) {
+	public function testFetchOptionsFromRequest(
+		$expectedValuesDefaults, $expectedValues, $preferences, $inputParams
+	) {
+		// $defaults and $allFalse are just to make the expected values below
+		// shorter by hiding the background.
+
+		$page = TestingAccessWrapper::newFromObject(
+			$this->newSpecialPage()
+		);
+
+		$page->registerFilters();
+
+		// Does not consider $preferences, just wiki's defaults
+		$wikiDefaults = $page->getDefaultOptions()->getAllValues();
+
+		switch ( $expectedValuesDefaults ) {
+		case 'allFalse':
+			$allFalse = $wikiDefaults;
+
+			foreach ( $allFalse as $key => $value ) {
+				if ( $value === true ) {
+					$allFalse[$key] = false;
+				}
+			}
+
+			// This is not exposed on the form (only in preferences) so it
+			// respects the preference.
+			$allFalse['extended'] = true;
+
+			$expectedValues += $allFalse;
+			break;
+		case 'wikiDefaults':
+			$expectedValues += $wikiDefaults;
+			break;
+		default:
+			$this->fail( "Unknown \$expectedValuesDefaults: $expectedValuesDefaults" );
+		}
+
 		$page = TestingAccessWrapper::newFromObject(
 			$this->newSpecialPage()
 		);
@@ -90,43 +127,21 @@ class SpecialWatchlistTest extends SpecialPageTestBase {
 	}
 
 	public function provideFetchOptionsFromRequest() {
-		// $defaults and $allFalse are just to make the expected values below
-		// shorter by hiding the background.
-
-		$page = TestingAccessWrapper::newFromObject(
-			$this->newSpecialPage()
-		);
-
-		$page->registerFilters();
-
-		// Does not consider $preferences, just wiki's defaults
-		$wikiDefaults = $page->getDefaultOptions()->getAllValues();
-
-		$allFalse = $wikiDefaults;
-
-		foreach ( $allFalse as $key => &$value ) {
-			if ( $value === true ) {
-				$value = false;
-			}
-		}
-
-		// This is not exposed on the form (only in preferences) so it
-		// respects the preference.
-		$allFalse['extended'] = true;
-
 		return [
-			[
-				[
+			'ignores casing' => [
+				'expectedValuesDefaults' => 'wikiDefaults',
+				'expectedValues' => [
 					'hideminor' => true,
-				] + $wikiDefaults,
-				[],
-				[
+				],
+				'preferences' => [],
+				'inputParams' => [
 					'hideMinor' => 1,
 				],
 			],
 
-			[
-				[
+			'first two same as prefs, second two overriden' => [
+				'expectedValuesDefaults' => 'wikiDefaults',
+				'expectedValues' => [
 					// First two same as prefs
 					'hideminor' => true,
 					'hidebots' => false,
@@ -135,38 +150,38 @@ class SpecialWatchlistTest extends SpecialPageTestBase {
 					'hideanons' => false,
 					'hideliu' => true,
 					'userExpLevel' => 'registered'
-				] + $wikiDefaults,
-				[
+				],
+				'preferences' => [
 					'watchlisthideminor' => 1,
 					'watchlisthidebots' => 0,
 
 					'watchlisthideanons' => 1,
 					'watchlisthideliu' => 0,
 				],
-				[
+				'inputParams' => [
 					'hideanons' => 0,
 					'hideliu' => 1,
 				],
 			],
 
-			// Defaults/preferences for form elements are entirely ignored for
-			// action=submit and omitted elements become false
-			[
-				[
+			'Defaults/preferences for form elements are entirely ignored for '
+			. 'action=submit and omitted elements become false' => [
+				'expectedValuesDefaults' => 'allFalse',
+				'expectedValues' => [
 					'hideminor' => false,
 					'hidebots' => true,
 					'hideanons' => false,
 					'hideliu' => true,
 					'userExpLevel' => 'unregistered'
-				] + $allFalse,
-				[
+				],
+				'preferences' => [
 					'watchlisthideminor' => 0,
 					'watchlisthidebots' => 1,
 
 					'watchlisthideanons' => 0,
 					'watchlisthideliu' => 1,
 				],
-				[
+				'inputParams' => [
 					'hidebots' => 1,
 					'hideliu' => 1,
 					'action' => 'submit',