diff --git a/packages/apollo-collaboration-server/src/files/filesUtil.ts b/packages/apollo-collaboration-server/src/files/filesUtil.ts
index ce959c66..a267ea2a 100644
--- a/packages/apollo-collaboration-server/src/files/filesUtil.ts
+++ b/packages/apollo-collaboration-server/src/files/filesUtil.ts
@@ -121,9 +121,9 @@ export class LocalFileGzip implements GenericFilehandle {
     const unzippedContents = await this.contents
     const bytesRead = unzippedContents.copy(
       buffer,
-      position,
       offset,
-      offset + length,
+      position,
+      position + length,
     )
     return { bytesRead, buffer }
   }