diff --git a/Tiltfile b/Tiltfile
index b2610550d..435d3649d 100644
--- a/Tiltfile
+++ b/Tiltfile
@@ -448,7 +448,7 @@ docker_build(
 
     # ignore local node_modules (in case they're present)
     ignore = ["./ethereum/node_modules"],
-
+    build_args = {"num_guardians": str(num_guardians)},
     # sync external scripts for incremental development
     # (everything else needs to be restarted from scratch for determinism)
     #