diff --git a/types/stylelint-webpack-plugin/index.d.ts b/types/stylelint-webpack-plugin/index.d.ts
index 87c3c261d6..52def71805 100644
--- a/types/stylelint-webpack-plugin/index.d.ts
+++ b/types/stylelint-webpack-plugin/index.d.ts
@@ -38,7 +38,7 @@ declare namespace StylelintWebpackPlugin {
         context?: string;
         emitErrors?: boolean;
         failOnError?: boolean;
-        files?: string[];
+        files?: string|string[];
         formatter?: Formatter;
         lintDirtyModulesOnly?: boolean;
         syntax?: string;