diff --git a/action.yml b/action.yml
index fb1a12e..69b1bb5 100644
--- a/action.yml
+++ b/action.yml
@@ -8,7 +8,7 @@ inputs:
     description: |-
       The Google Cloud Project ID. If unspecified, it is inherited from the
       environment.
-    required: true
+    required: false
 
   working_directory:
     description: |-