diff --git a/src/index.d.ts b/src/index.d.ts
index 77a88e03cf..ec32771da2 100644
--- a/src/index.d.ts
+++ b/src/index.d.ts
@@ -47,6 +47,7 @@ declare namespace admin {
     databaseAuthVariableOverride?: Object;
     databaseURL?: string;
     storageBucket?: string;
+    projectId?: string;
   }
 
   var SDK_VERSION: string;