diff --git a/Makefile.builder b/Makefile.builder
index 23827af..30e4cec 100644
--- a/Makefile.builder
+++ b/Makefile.builder
@@ -3,5 +3,6 @@ OCAML_VERSION ?= 4.08.1
 SOURCE_BUILD_DEP := firewall-build-dep
 
 firewall-build-dep:
-	opam pin -y add mirage 3.5.2
+	opam install -y depext
+	opam depext -i -y mirage.3.7.4 lwt.4.5.0