diff --git a/make.sh b/make.sh
index 3a1c1c0c..f29c7b06 100755
--- a/make.sh
+++ b/make.sh
@@ -17,7 +17,7 @@ ocb() {
 opam_setup() {
   set -x
   opam init -y -a --bare $SANDBOXING # sandboxing is disabled in travis and docker
-  opam switch -y create ./ --deps-only ocaml-base-compiler.4.07.1
+  opam switch -y create ./ --deps-only --locked ocaml-base-compiler.4.07.1
   # opam install camlp4 mongo # camlp4 needed for mongo
 }