diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index ab038dc43..974c49b97 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -5,6 +5,7 @@ variables:
   public_docker_image: docker.io/${CI_PROJECT_PATH}
 
 stages:
+  - precheck
   - prepare
   - build_deps
   - build
@@ -14,6 +15,17 @@ stages:
   - deploy
   - cleanup
 
+## Check zeronet/alphanet
+
+precheck:constant:
+  image: ${opam_image}
+  stage: precheck
+  only:
+    - zeronet
+    - alphanet
+  script:
+    - ./scripts/check_patch.sh "${CI_COMMIT_REF_NAME}"
+
 ## Template for `docker_in_docker` jobs
 
 .dind_template: &dind_definition
@@ -56,7 +68,6 @@ build_deps:
 .build_deps_template: &build_deps_definition
   image: ${build_deps_image}:${CI_COMMIT_SHA}
   before_script:
-    - ./scripts/apply_patch.sh "${CI_COMMIT_REF_NAME}"
     - opam list
   tags:
     - gitlab-org
@@ -456,7 +467,6 @@ publish:docker:minimal:
     - alphanet
     - zeronet
   script:
-    - ./scripts/apply_patch.sh "${CI_COMMIT_REF_NAME}" ;
     - ./scripts/ci/create_docker_image.build.sh
         "tezos_build" "${CI_COMMIT_REF_NAME}"
         "${build_deps_image}:${CI_COMMIT_SHA}"
@@ -481,7 +491,6 @@ publish:github:
     - echo "${CI_PK_GITHUB}" > ~/.ssh/id_rsa
     - chmod 400 ~/.ssh/id_rsa
     - rm -fr .git/refs/original
-    - ./scripts/apply_patch.sh "${CI_COMMIT_REF_NAME}" ;
     - sudo apk add --no-cache openssh
     - git push git@github.com:tezos/tezos.git -f HEAD:${CI_COMMIT_REF_NAME}
   tags:
diff --git a/scripts/apply_patch.sh b/scripts/apply_patch.sh
index fbd543b67..437fc4957 100755
--- a/scripts/apply_patch.sh
+++ b/scripts/apply_patch.sh
@@ -21,13 +21,13 @@ case "$branch" in
         sed -i s/TEZOS/TEZOS_ZERONET/ ./src/lib_shell/distributed_db_message.ml
         patch -p1 < scripts/alphanet_constants.patch
         patch -p1 < scripts/zeronet.patch
-        if has_git; then git commit -a -m "Zeronet: DO NOT MERGE" --author "Tezos CI <null@tezos.com>"; fi
+        if has_git; then git commit -a -m "Zeronet: change economic constants." --author "Tezos CI <null@tezos.com>"; fi
         echo "Done"
         ;;
     alphanet)
         sed -i s/TEZOS/TEZOS_ALPHANET/ ./src/lib_shell/distributed_db_message.ml
         patch -p1 < scripts/alphanet_constants.patch
-        if has_git; then git commit -a -m "Alphanet: DO NOT MERGE" --author "Tezos CI <null@tezos.com>"; fi
+        if has_git; then git commit -a -m "Alphanet: change economic constants." --author "Tezos CI <null@tezos.com>"; fi
         echo "Done"
         ;;
     *)
diff --git a/scripts/check_patch.sh b/scripts/check_patch.sh
new file mode 100755
index 000000000..c8ca53209
--- /dev/null
+++ b/scripts/check_patch.sh
@@ -0,0 +1,22 @@
+#! /bin/sh
+
+set -e
+
+if [ $1 != "zeronet" ] && [ $1 != "alphanet" ] ; then
+    echo Ignored
+    exit 0
+fi
+
+if git log | grep "net: change economic constants" >/dev/null 2>&1 ; then
+    echo OK
+    exit 0
+fi
+
+cat <<EOF
+
+The branch $1 should include the constant patch.
+Please run './scripts/apply-patch.sh $1'.
+
+EOF
+
+exit 1