diff --git a/sha1/tsconfig.json b/sha1/tsconfig.json
index 81a2585b1f..ec99de7c10 100644
--- a/sha1/tsconfig.json
+++ b/sha1/tsconfig.json
@@ -3,6 +3,7 @@
         "module": "commonjs",
         "target": "es6",
         "noImplicitAny": true,
+        "noImplicitThis": true,
         "strictNullChecks": false,
         "baseUrl": "../",
         "typeRoots": [