diff --git a/types/eslint/index.d.ts b/types/eslint/index.d.ts
index 451477af40..01f39ee83e 100644
--- a/types/eslint/index.d.ts
+++ b/types/eslint/index.d.ts
@@ -471,7 +471,7 @@ export class CLIEngine {
 
     isPathIgnored(filePath: string): boolean;
 
-    getFormatter(format: string): CLIEngine.Formatter;
+    getFormatter(format?: string): CLIEngine.Formatter;
 
     getRules(): Map<string, Rule.RuleModule>;