diff --git a/includes/resourceloader/ResourceLoaderSkinModule.php b/includes/resourceloader/ResourceLoaderSkinModule.php
index dd831114424..de22650c832 100644
--- a/includes/resourceloader/ResourceLoaderSkinModule.php
+++ b/includes/resourceloader/ResourceLoaderSkinModule.php
@@ -246,9 +246,12 @@ class ResourceLoaderSkinModule extends ResourceLoaderLessVarFileModule {
 
 		$listMode = false;
 		foreach ( $features as $key => $enabled ) {
-			// TODO: Restore feature key validation (T271441)
 			if ( is_string( $enabled ) ) {
 				$listMode = true;
+				$key = $enabled;
+			}
+			if ( !isset( self::FEATURE_FILES[$key] ) ) {
+				throw new InvalidArgumentException( "Feature '$key' is not recognised" );
 			}
 		}
 
diff --git a/tests/phpunit/includes/resourceloader/ResourceLoaderSkinModuleTest.php b/tests/phpunit/includes/resourceloader/ResourceLoaderSkinModuleTest.php
index 1f73fd8ed8b..00e3925f7ec 100644
--- a/tests/phpunit/includes/resourceloader/ResourceLoaderSkinModuleTest.php
+++ b/tests/phpunit/includes/resourceloader/ResourceLoaderSkinModuleTest.php
@@ -579,4 +579,38 @@ CSS
 			array_values( $actual )
 		);
 	}
+
+	public static function provideInvalidFeatures() {
+		yield 'listed unknown' => [
+			[ 'logo', 'unknown' ],
+		];
+
+		yield 'enabled unknown' => [
+			[
+				'logo' => true,
+				'toc' => false,
+				'unknown' => true,
+			],
+		];
+
+		yield 'disbled unknown' => [
+			[
+				'logo' => true,
+				'toc' => false,
+				'unknown' => false,
+			],
+		];
+	}
+
+	/**
+	 * @covers ResourceLoaderSkinModule
+	 * @dataProvider provideInvalidFeatures
+	 */
+	public function testConstructInvalidFeatures( array $features ) {
+		$this->expectException( InvalidArgumentException::class );
+		$this->expectExceptionMessage( "Feature 'unknown' is not recognised" );
+		$module = new ResourceLoaderSkinModule( [
+			'features' => $features,
+		] );
+	}
 }