diff --git a/.ci-macosx.sh b/.ci-macosx.sh
index ea6d44cb1..b793b0d7a 100644
--- a/.ci-macosx.sh
+++ b/.ci-macosx.sh
@@ -6,7 +6,7 @@ brew update
 brew install pkg-config
 brew install opam
 brew install libev
-opam init -y --compiler=4.05.0
+opam init -y --compiler=4.12.0
 eval $(opam env)
 
 opam install -y -j 2 . --deps-only --locked
diff --git a/.github/workflows/static-builds.yml b/.github/workflows/static-builds.yml
index 02b1c868c..a87fffebd 100644
--- a/.github/workflows/static-builds.yml
+++ b/.github/workflows/static-builds.yml
@@ -46,20 +46,16 @@ jobs:
           sw_vers
           system_profiler SPSoftwareDataType
           uname -a
-      # Need unreleased 2.1.0~rc
-      # - name: Retrieve opam
-      #   run: |
-      #     mkdir "$HOME/bin"
-      #     wget https://github.com/ocaml/opam/releases/download/2.1.0-beta2/opam-2.1.0-beta2-x86_64-macos -O $HOME/bin/opam
-      #     chmod a+x $HOME/bin/opam
-      #     echo "$HOME/bin" >> $GITHUB_PATH
-      - name: Install latest opam
+      - name: Retrieve opam
         run: |
-          brew install opam --HEAD
+          mkdir "$HOME/bin"
+          wget https://github.com/ocaml/opam/releases/download/2.1.0/opam-2.1.0-x86_64-macos -O $HOME/bin/opam
+          chmod a+x $HOME/bin/opam
+          echo "$HOME/bin" >> $GITHUB_PATH
       - name: Prepare build environment
         run: |
           opam init -a --bare
-          opam switch create . ocaml-base-compiler 'dune<2' --deps-only
+          opam switch create . ocaml-base-compiler --deps-only
       - name: Build the binaries
         run: |
           opam exec -- make LINKING_MODE=static
diff --git a/Dockerfile b/Dockerfile
index c9e6079b7..00e6fd143 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM ocaml/opam2:alpine as compilation
+FROM ocaml/opam:alpine-3.13-ocaml-4.12 as compilation
 LABEL Description="learn-ocaml building" Vendor="OCamlPro"
 
 WORKDIR /home/opam/learn-ocaml
@@ -42,7 +42,7 @@ WORKDIR /learnocaml
 
 COPY --from=compilation /home/opam/install-prefix/bin/learn-ocaml-client /usr/bin
 
-ENTRYPOINT ["dumb-init","learn-ocaml-client"]
+ENTRYPOINT ["dumb-init","/usr/bin/learn-ocaml-client"]
 
 LABEL org.opencontainers.image.title="learn-ocaml-client"
 LABEL org.opencontainers.image.description="learn-ocaml command-line client"
@@ -68,7 +68,7 @@ WORKDIR /home/learn-ocaml
 
 COPY --from=compilation /home/opam/install-prefix /usr
 
-ENTRYPOINT ["dumb-init","learn-ocaml","--sync-dir=/sync","--repo=/repository"]
+ENTRYPOINT ["dumb-init","/usr/bin∕learn-ocaml","--sync-dir=/sync","--repo=/repository"]
 CMD ["build","serve"]
 
 LABEL org.opencontainers.image.title="learn-ocaml"
diff --git a/Dockerfile.test-client b/Dockerfile.test-client
index ee7c49a13..32345200a 100644
--- a/Dockerfile.test-client
+++ b/Dockerfile.test-client
@@ -1,7 +1,7 @@
 # This Dockerfile is useful for testing purposes
 # to ensure learn-ocaml-client can be built alone from learn-ocaml-client.opam
 
-FROM ocaml/opam:alpine-3.13-ocaml-4.05 as compilation
+FROM ocaml/opam:alpine-3.13-ocaml-4.12 as compilation
 LABEL Description="learn-ocaml building" Vendor="OCamlPro"
 
 WORKDIR learn-ocaml
@@ -13,7 +13,7 @@ RUN sudo chown -R opam:nogroup .
 ENV OPAMYES true
 RUN echo 'archive-mirrors: [ "https://opam.ocaml.org/cache" ]' >> ~/.opam/config \
   && opam repository set-url default http://opam.ocaml.org \
-  && opam switch 4.05 \
+  && opam switch 4.12 \
   && echo 'pre-session-commands: [ "sudo" "apk" "add" depexts ]' >> ~/.opam/config \
   && opam pin add -n -y -k path learn-ocaml-client . \
   && opam install learn-ocaml-client --deps-only
diff --git a/Makefile b/Makefile
index 22faba759..096b20344 100644
--- a/Makefile
+++ b/Makefile
@@ -95,7 +95,7 @@ travis: # From https://stackoverflow.com/questions/21053657/how-to-run-travis-ci
 static-binaries:
 	./scripts/static-build.sh
 
-BINARIES = src/main/learnocaml_client.bc src/main/learnocaml_main.bc src/main/learnocaml_server_main.exe
+BINARIES = src/main/learnocaml_client.exe src/main/learnocaml_main.exe src/main/learnocaml_server_main.exe
 
 .PHONY: detect-libs
 detect-libs:
@@ -104,6 +104,7 @@ detect-libs:
 	baseid="detect-libs.$$$$"; echo ...; \
 	$(MAKE) LINKING_MODE=dynamic OCAMLPARAM="_,verbose=1" > $$baseid.log 2>&1; \
 	for bin in $(BINARIES); do \
+	  rm -f "_build/default/$$bin"; \
 	  base=$${bin#src/main/}; base=$${base%.*}; \
 	  grep -e "'$$bin'" $$baseid.log > $$baseid.$$base.log; \
 	  printf "%s: " "$$base"; \
diff --git a/learn-ocaml-client.opam.locked b/learn-ocaml-client.opam.locked
new file mode 100644
index 000000000..e6c67f20b
--- /dev/null
+++ b/learn-ocaml-client.opam.locked
@@ -0,0 +1,107 @@
+opam-version: "2.0"
+name: "learn-ocaml-client"
+version: "0.12"
+synopsis: "The learn-ocaml client"
+description: """\
+This contains the binaries to interact with the learn-ocaml
+platform from the command line."""
+maintainer: "Yann Régis-Gianas"
+authors: [
+  "Benjamin Canou (OCamlPro)"
+  "Çağdaş Bozman (OCamlPro)"
+  "Grégoire Henry (OCamlPro)"
+  "Louis Gesbert (OCamlPro)"
+  "Pierrick Couderc (OCamlPro)"
+]
+license: "MIT"
+homepage: "https://github.com/ocaml-sf/learn-ocaml"
+bug-reports: "https://github.com/ocaml-sf/learn-ocaml/issues"
+depends: [
+  "angstrom" {= "0.15.0"}
+  "asak" {= "0.3"}
+  "astring" {= "0.8.5"}
+  "base" {= "v0.14.1"}
+  "base-bigarray" {= "base"}
+  "base-bytes" {= "base"}
+  "base-threads" {= "base"}
+  "base-unix" {= "base"}
+  "base64" {= "3.5.0"}
+  "bigarray-compat" {= "1.0.0"}
+  "bigstringaf" {= "0.8.0"}
+  "biniou" {= "1.2.1"}
+  "cmdliner" {= "1.0.4"}
+  "cohttp" {= "4.0.0"}
+  "cohttp-lwt" {= "4.0.0"}
+  "cohttp-lwt-unix" {= "4.0.0"}
+  "conduit" {= "1.3.0"}
+  "conduit-lwt" {= "1.3.0"}
+  "conduit-lwt-unix" {= "1.3.0"}
+  "conf-libssl" {= "3"}
+  "conf-pkg-config" {= "2"}
+  "conf-which" {= "1"}
+  "cppo" {= "1.6.7"}
+  "csexp" {= "1.5.1"}
+  "cstruct" {= "5.0.0"}
+  "digestif" {= "1.0.0"}
+  "dune" {= "2.9.0"}
+  "dune-configurator" {= "2.9.0"}
+  "easy-format" {= "1.3.2"}
+  "eqaf" {= "0.7"}
+  "ezjsonm" {= "1.1.0"}
+  "fieldslib" {= "v0.14.0"}
+  "fmt" {= "0.8.9"}
+  "gg" {= "0.9.3"}
+  "hex" {= "1.4.0"}
+  "ipaddr" {= "2.8.0"}
+  "jbuilder" {= "1.0+beta20.2"}
+  "js_of_ocaml" {= "3.9.0"}
+  "js_of_ocaml-compiler" {= "3.9.1"}
+  "js_of_ocaml-ppx" {= "3.9.0"}
+  "jsonm" {= "1.0.1"}
+  "logs" {= "0.7.0"}
+  "lwt" {= "5.4.1"}
+  "lwt_ssl" {= "1.1.3"}
+  "magic-mime" {= "1.1.3"}
+  "menhir" {= "20210419"}
+  "menhirLib" {= "20210419"}
+  "menhirSdk" {= "20210419"}
+  "mmap" {= "1.1.0"}
+  "num" {= "1.4"}
+  "ocaml" {= "4.12.0"}
+  "ocaml-compiler-libs" {= "v0.12.3"}
+  "ocaml-config" {= "2"}
+  "ocaml-migrate-parsetree" {= "1.8.0"}
+  "ocaml-options-vanilla" {= "1"}
+  "ocaml-syntax-shims" {= "1.0.0"}
+  "ocamlbuild" {= "0.14.0"}
+  "ocamlfind" {= "1.9.1"}
+  "ocp-indent-nlfork" {= "1.5.4"}
+  "ocp-ocamlres" {= "0.4"}
+  "ocplib-endian" {= "1.1"}
+  "ocplib-json-typed" {= "0.7.1"}
+  "omd" {= "1.3.1"}
+  "parsexp" {= "v0.14.1"}
+  "pprint" {= "20200410"}
+  "ppx_derivers" {= "1.2.1"}
+  "ppx_fields_conv" {= "v0.14.1"}
+  "ppx_sexp_conv" {= "v0.14.1"}
+  "ppx_tools" {= "6.3"}
+  "ppxlib" {= "0.15.0"}
+  "re" {= "1.9.0"}
+  "result" {= "1.5"}
+  "seq" {= "0.2.2"}
+  "sexplib" {= "v0.14.0"}
+  "sexplib0" {= "v0.14.0"}
+  "ssl" {= "0.5.5"}
+  "stdlib-shims" {= "0.3.0"}
+  "stringext" {= "1.6.0"}
+  "topkg" {= "1.0.3"}
+  "uchar" {= "0.0.2"}
+  "uri" {= "4.2.0"}
+  "uri-sexp" {= "4.2.0"}
+  "uutf" {= "1.0.2"}
+  "vg" {= "0.9.4"}
+  "yojson" {= "1.7.0"}
+]
+build: ["dune" "build" "@install" "-p" name "-j" jobs]
+dev-repo: "git+https://github.com/ocaml-sf/learn-ocaml"
diff --git a/learn-ocaml.opam.locked b/learn-ocaml.opam.locked
index c402ccabd..40f7a6ef0 100644
--- a/learn-ocaml.opam.locked
+++ b/learn-ocaml.opam.locked
@@ -74,7 +74,6 @@ depends: [
   "mmap" {= "1.1.0"}
   "num" {= "1.4"}
   "ocaml" {= "4.12.0"}
-  "ocaml-base-compiler" {= "4.12.0"}
   "ocaml-compiler-libs" {= "v0.12.3"}
   "ocaml-config" {= "2"}
   "ocaml-migrate-parsetree" {= "1.8.0"}
diff --git a/scripts/static-build.sh b/scripts/static-build.sh
index adbddf9a5..f336e7f2e 100755
--- a/scripts/static-build.sh
+++ b/scripts/static-build.sh
@@ -10,11 +10,11 @@ cd $(dirname "$0")/..
 set -o pipefail
 git ls-files -z | xargs -0 tar c | \
   docker run --rm -i \
-    ocamlpro/ocaml:4.05 \
+    ocamlpro/ocaml:4.12-2021-07-25 \
     sh -uexc \
       'tar x >&2 &&
-       sudo apk add openssl-libs-static >&2 &&
-       opam switch create . ocaml-system "dune<2" --deps-only >&2 &&
+       sudo apk add openssl-libs-static bash >&2 &&
+       opam switch create . ocaml-system --deps-only --locked >&2 &&
        opam exec make LINKING_MODE=static >&2 &&
        tar c -hC _build/install/default/bin .' | \
   tar vx
diff --git a/src/main/dune b/src/main/dune
index eab003c95..7d4e4bbb5 100644
--- a/src/main/dune
+++ b/src/main/dune
@@ -56,7 +56,7 @@
 (rule
   (targets linking_main.sexp)
   (action  (with-stdout-to %{targets}
-    (run ./linking_flags.sh %{env:LINKING_MODE=dynamic} %{ocaml-config:system} laolao_stubs threads camlrun))))
+    (run ./linking_flags.sh %{env:LINKING_MODE=dynamic} %{ocaml-config:system} checkseum_c_stubs threads camlrun))))
 (rule
   (targets linking_client.sexp)
   (action  (with-stdout-to %{targets}
@@ -64,4 +64,4 @@
 (rule
   (targets linking_server.sexp)
   (action  (with-stdout-to %{targets}
-    (run ./linking_flags.sh %{env:LINKING_MODE=dynamic} -- laolao_stubs threadsnat))))
+    (run ./linking_flags.sh %{env:LINKING_MODE=dynamic} -- checkseum_c_stubs threadsnat))))
diff --git a/src/main/linking_flags.sh b/src/main/linking_flags.sh
index 514840d74..f019eb7ea 100755
--- a/src/main/linking_flags.sh
+++ b/src/main/linking_flags.sh
@@ -43,18 +43,21 @@ case $(uname -s) in
     Linux)
         case $(. /etc/os-release && echo $ID) in
             alpine)
-                COMMON_LIBS="camlstr base_stubs ssl_threads_stubs ssl crypto cstruct_stubs lwt_unix_stubs bigarray unix c"
+                COMMON_LIBS="camlstr ssl_threads_stubs ssl crypto cstruct_stubs bigstringaf_stubs lwt_unix_stubs unix c"
                 # `m` and `pthread` are built-in musl
                 echo '(-noautolink'
+                echo ' -verbose'
                 echo ' -cclib -Wl,-Bstatic'
                 echo ' -cclib -static-libgcc'
+                # checkseum requires an additional `-L` argument
+                ocamlfind query -l-format checkseum.c
                 for l in $EXTRA_LIBS $COMMON_LIBS; do
                     echo " -cclib -l$l"
                 done
                 echo ' -cclib -static)'
                 ;;
             *)
-                echo "Error: static linking is only supported in Alpine, to avoids glibc constraints" >&2
+                echo "Error: static linking is only supported in Alpine, to avoids glibc constraints (use scripts/static-build.sh to build through an Alpine Docker container)" >&2
                 exit 3
         esac
         ;;
@@ -62,6 +65,7 @@ case $(uname -s) in
         COMMON_LIBS="camlstr base_stubs ssl_threads_stubs /usr/local/opt/openssl/lib/libssl.a /usr/local/opt/openssl/lib/libcrypto.a cstruct_stubs lwt_unix_stubs bigarray unix"
         # `m` and `pthread` are built-in in libSystem
         echo '(-noautolink'
+        echo ' -verbose'
         for l in $EXTRA_LIBS $COMMON_LIBS; do
             if [ "${l%.a}" != "${l}" ]; then echo " -cclib $l"
             else echo " -cclib -l$l"