diff --git a/index.d.ts b/index.d.ts
index 947823f..bae3eef 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -11,7 +11,7 @@ interface Chunk {
   readonly bytes: number;
 }
 interface Options {
-  readonly isHTML: false;
+  readonly isHTML: boolean;
   readonly languageHint: string;
   readonly encodingHint: string;
   readonly tldHint: string;
@@ -28,4 +28,4 @@ export declare module 'cld' {
   declare function detect(text: string, callback: (err: string, result: DetectLanguage) => void): void;
   declare function detect(text: string, options: Options): Promise<DetectLanguage>;
   declare function detect(text: string): Promise<DetectLanguage>;
-}
\ No newline at end of file
+}