diff --git a/.gitlab-ci/run-check-todos.sh b/.gitlab-ci/run-check-todos.sh
index 8a6a9bfda..e2df10ef5 100755
--- a/.gitlab-ci/run-check-todos.sh
+++ b/.gitlab-ci/run-check-todos.sh
@@ -2,29 +2,6 @@
 
 set -e
 
-ancestor_horizon=28  # days (4 weeks)
-
-# We need to add a new remote for the upstream target branch, since this script
-# could be running in a personal fork of the repository which has out of date
-# branches.
-#
-# Limit the fetch to a certain date horizon to limit the amount of data we get.
-# If the branch was forked from origin/master before this horizon, it should
-# probably be rebased.
-git remote add upstream https://gitlab.gnome.org/GNOME/glib.git
-git fetch --shallow-since="$(date --date="${ancestor_horizon} days ago" +%Y-%m-%d)" upstream
-
-# Work out the newest common ancestor between the detached HEAD that this CI job
-# has checked out, and the upstream target branch (which will typically be
-# `upstream/master` or `upstream/glib-2-62`).
-# `${CI_MERGE_REQUEST_TARGET_BRANCH_NAME}` is only defined if we’re running in
-# a merge request pipeline; fall back to `${CI_DEFAULT_BRANCH}` otherwise.
-newest_common_ancestor_sha=$(diff --old-line-format='' --new-line-format='' <(git rev-list --first-parent "upstream/${CI_MERGE_REQUEST_TARGET_BRANCH_NAME:-${CI_DEFAULT_BRANCH}}") <(git rev-list --first-parent HEAD) | head -1)
-if [ -z "${newest_common_ancestor_sha}" ]; then
-    echo "Couldn’t find common ancestor with upstream master. This typically"
-    echo "happens if you branched from master a long time ago. Please update"
-    echo "your clone, rebase, and re-push your branch."
-    exit 1
-fi
+source .gitlab-ci/search-common-ancestor.sh
 
 ./.gitlab-ci/check-todos.py "${newest_common_ancestor_sha}"
diff --git a/.gitlab-ci/run-style-check-diff.sh b/.gitlab-ci/run-style-check-diff.sh
index b308e7679..a04bd0731 100755
--- a/.gitlab-ci/run-style-check-diff.sh
+++ b/.gitlab-ci/run-style-check-diff.sh
@@ -7,29 +7,7 @@ ancestor_horizon=28  # days (4 weeks)
 # Wrap everything in a subshell so we can propagate the exit status.
 (
 
-# We need to add a new remote for the upstream target branch, since this script
-# could be running in a personal fork of the repository which has out of date
-# branches.
-#
-# Limit the fetch to a certain date horizon to limit the amount of data we get.
-# If the branch was forked from origin/master before this horizon, it should
-# probably be rebased.
-git remote add upstream https://gitlab.gnome.org/GNOME/glib.git
-git fetch --shallow-since="$(date --date="${ancestor_horizon} days ago" +%Y-%m-%d)" upstream
-
-# Work out the newest common ancestor between the detached HEAD that this CI job
-# has checked out, and the upstream target branch (which will typically be
-# `upstream/master` or `upstream/glib-2-62`).
-#
-# `${CI_MERGE_REQUEST_TARGET_BRANCH_NAME}` is only defined if we’re running in
-# a merge request pipeline; fall back to `${CI_DEFAULT_BRANCH}` otherwise.
-newest_common_ancestor_sha=$(diff --old-line-format='' --new-line-format='' <(git rev-list --first-parent "upstream/${CI_MERGE_REQUEST_TARGET_BRANCH_NAME:-${CI_DEFAULT_BRANCH}}") <(git rev-list --first-parent HEAD) | head -1)
-if [ -z "${newest_common_ancestor_sha}" ]; then
-    echo "Couldn’t find common ancestor with upstream master. This typically"
-    echo "happens if you branched from master a long time ago. Please update"
-    echo "your clone, rebase, and re-push your branch."
-    exit 1
-fi
+source .gitlab-ci/search-common-ancestor.sh
 
 git diff -U0 --no-color "${newest_common_ancestor_sha}" | ./clang-format-diff.py -binary "clang-format-7" -p1
 
diff --git a/.gitlab-ci/search-common-ancestor.sh b/.gitlab-ci/search-common-ancestor.sh
new file mode 100755
index 000000000..d09f7d3f8
--- /dev/null
+++ b/.gitlab-ci/search-common-ancestor.sh
@@ -0,0 +1,28 @@
+#!/bin/bash
+
+set -e
+
+ancestor_horizon=28  # days (4 weeks)
+
+# We need to add a new remote for the upstream target branch, since this script
+# could be running in a personal fork of the repository which has out of date
+# branches.
+#
+# Limit the fetch to a certain date horizon to limit the amount of data we get.
+# If the branch was forked from origin/master before this horizon, it should
+# probably be rebased.
+git remote add upstream https://gitlab.gnome.org/GNOME/glib.git
+git fetch --shallow-since="$(date --date="${ancestor_horizon} days ago" +%Y-%m-%d)" upstream
+
+# Work out the newest common ancestor between the detached HEAD that this CI job
+# has checked out, and the upstream target branch (which will typically be
+# `upstream/master` or `upstream/glib-2-62`).
+# `${CI_MERGE_REQUEST_TARGET_BRANCH_NAME}` is only defined if we’re running in
+# a merge request pipeline; fall back to `${CI_DEFAULT_BRANCH}` otherwise.
+newest_common_ancestor_sha=$(diff --old-line-format='' --new-line-format='' <(git rev-list --first-parent "upstream/${CI_MERGE_REQUEST_TARGET_BRANCH_NAME:-${CI_DEFAULT_BRANCH}}") <(git rev-list --first-parent HEAD) | head -1)
+if [ -z "${newest_common_ancestor_sha}" ]; then
+    echo "Couldn’t find common ancestor with upstream master. This typically"
+    echo "happens if you branched from master a long time ago. Please update"
+    echo "your clone, rebase, and re-push your branch."
+    exit 1
+fi