diff --git a/lwt_ppx_let.opam b/lwt_ppx_let.opam
index 845fafcee..724f60441 100644
--- a/lwt_ppx_let.opam
+++ b/lwt_ppx_let.opam
@@ -25,4 +25,8 @@ depends: [
   "ocaml" {>= "4.08"}
 ]
 
+pin-depends: [
+  [ "base.v0.15.1" "git+https://github.com/dra27/base.git#41c109168efd44ff2c901006e577beb609490ffc" ]
+]
+
 description: "Internal package used to partition ppx_let tests."