diff --git a/Dockerfile b/Dockerfile
index 39f4137..fd03af4 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -31,7 +31,7 @@ RUN sudo mkdir -p /usr/local/bin \
     && sudo chmod a+x /usr/local/bin/man2html
 RUN sudo mv /usr/bin/opam-2.1 /usr/bin/opam && opam update
 RUN opam install odoc
-RUN git clone https://github.com/ocaml/opam --single-branch --depth 1 --branch master /home/opam/opam
+RUN git clone https://github.com/ocaml/opam --single-branch --depth 1 --branch 2.1 /home/opam/opam
 WORKDIR /home/opam/opam
 RUN opam exec -- ./configure --without-mccs && opam exec -- make lib-ext && opam exec -- make
 RUN echo '(vendored_dirs src_ext)' >> dune