diff --git a/install/scripts/install_ocaml.sh b/install/scripts/install_ocaml.sh
index b3dd0db..e08ef6c 100755
--- a/install/scripts/install_ocaml.sh
+++ b/install/scripts/install_ocaml.sh
@@ -4,7 +4,7 @@ set -u
 set -e
 
 cd .. ; QMCCHEM_PATH="$PWD" ; cd -
-PACKAGES="cryptokit ocamlbuild getopt ocamlfind sexplib.v0.11.0 ppx_sexp_conv ppx_deriving"
+PACKAGES="cryptokit ocamlbuild getopt ocamlfind sexplib ppx_sexp_conv ppx_deriving"
 
 # return 0 if program version is equal or greater than check version
 check_version () {
@@ -91,7 +91,7 @@ export LD_LIBRARY_PATH="${QMCCHEM_PATH}/lib:${LD_LIBRARY_PATH}"
 export LIBRARY_PATH="${QMCCHEM_PATH}/lib:${LIBRARY_PATH}"
 export C_INCLUDE_PATH="${QMCCHEM_PATH}/lib:${C_INCLUDE_PATH}"
 set -u
-opam install --unlock-base ${PACKAGES}
+opam install -y --unlock-base ${PACKAGES} || exit 3
 rm "${QMCCHEM_PATH}"/install/_build/ocaml.log
 exit 0