diff --git a/src/jbuild b/src/jbuild
index 6c9d6e805..b066e515f 100644
--- a/src/jbuild
+++ b/src/jbuild
@@ -2,6 +2,7 @@
  ((name ppx_let)
   (public_name ppx_let)
   (kind ppx_rewriter)
+  (flags (:standard -safe-string))
   (libraries (ppx_core ppx_driver))
   (preprocess no_preprocessing)))