diff --git a/cluster/Dockerfile b/cluster/Dockerfile
index e222f084..9089e92f 100644
--- a/cluster/Dockerfile
+++ b/cluster/Dockerfile
@@ -1,7 +1,7 @@
 FROM ocaml/opam:debian-ocaml-4.13 AS build
 RUN sudo apt-get update && sudo apt-get install libc6-dev libev-dev capnproto m4 pkg-config libsqlite3-dev libgmp-dev libffi-dev -y --no-install-recommends
 RUN opam remote add origin 'https://opam.ocaml.org' --all-switches && opam remote remove default && opam update
-RUN opam install dune>=2.8 ppx_expect>=v0.14.1 prometheus ppx_sexp_conv dune-build-info lwt>=5.4.1 capnp-rpc-lwt>=1.2 capnp-rpc-net capnp-rpc-unix>=1.2 extunix>=0.3.2 logs conf-libev digestif>=0.8 fpath lwt-dllist prometheus-app>=1.1 cohttp-lwt-unix sqlite3 psq mirage-crypto>=0.8.5 ppx_deriving ppx_deriving_yojson astring fmt>=0.8.9 cmdliner tar-unix>=2.0.0 yojson sexplib sha
+RUN opam install dune>=2.8 ppx_expect>=v0.14.1 prometheus ppx_sexp_conv dune-build-info lwt>=5.4.1 capnp-rpc-lwt>=1.2 capnp-rpc-net capnp-rpc-unix>=1.2 extunix>=0.3.2 logs conf-libev digestif>=0.8 fpath lwt-dllist prometheus-app=1.1 cohttp-lwt-unix sqlite3 psq mirage-crypto>=0.8.5 ppx_deriving ppx_deriving_yojson astring fmt>=0.8.9 cmdliner tar-unix>=2.0.0 yojson sexplib sha
 RUN mkdir src && cd src && git clone 'https://github.com/ocurrent/ocluster' && opam pin -yn ocluster
 RUN cd src && git clone 'https://github.com/ocurrent/obuilder' && opam pin -yn obuilder
 WORKDIR src/ocluster
diff --git a/worker/cb-worker.opam b/worker/cb-worker.opam
index 733099de..904fd288 100644
--- a/worker/cb-worker.opam
+++ b/worker/cb-worker.opam
@@ -16,7 +16,7 @@ depends: [
   "ocluster-api"    {= "dev"}
   "obuilder"        {= "dev"}
   "obuilder-spec"   {= "dev"}
-  "prometheus-app"
+  "prometheus-app"  {= "1.1"}
   "fpath"
   "logs"
   "ocaml" {>= "4.08"}