diff --git a/Containerfile b/Containerfile
index 766ebb2..ccf0ea0 100644
--- a/Containerfile
+++ b/Containerfile
@@ -120,8 +120,10 @@ RUN git clone --depth=1 --recursive --branch=z3-4.13.3 https://git.libre-chip.or
 # https://rocq-prover.org/docs/using-opam#installing-rocq
 # https://github.com/rocq-community/docker-base/blob/71a2b78f4faf9c1dc658e1c4bf920dff2257787f/base/rocq-single/Dockerfile#L87 (BSD license)
 # https://gitlab.com/rocq-community/docker-rocq/-/blob/c4507ab5c137227700dac7e35fb5c0747fcd272f/rocq/stable/Dockerfile (MIT license)
-RUN opam init --auto-setup --yes --disable-sandboxing \
-    && eval $(opam env) \
+# initialize an "opam switch"
+RUN opam init --auto-setup --yes --disable-sandboxing
+# install Rocq inside the default switch
+RUN eval $(opam env) \
     && opam pin -y add rocq-prover 9.0.0 \
     && opam clean -a -r -c -s --logs
 ENV PATH=/root/.opam/default/bin:$PATH