diff --git a/index.d.ts b/index.d.ts
index b8e7a3b..c491d82 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -21,7 +21,7 @@ export interface DecodedSourceMap {
 export class SourceMap {
   constructor(properties: DecodedSourceMap);
 
-  version: string;
+  version: number;
   file: string;
   sources: string[];
   sourcesContent: string[];