diff --git a/CI/ubuntu_gcc_preprocess.sh b/CI/ubuntu_gcc_preprocess.sh
index d519d178aa..ed4e4320b3 100755
--- a/CI/ubuntu_gcc_preprocess.sh
+++ b/CI/ubuntu_gcc_preprocess.sh
@@ -50,15 +50,16 @@ git remote add target "${CI_MERGE_REQUEST_PROJECT_URL:-https://gitlab.com/OpenMW
 
 TARGET_BRANCH="${CI_MERGE_REQUEST_TARGET_BRANCH_NAME:-master}"
 
-git fetch target "${TARGET_BRANCH:?}"
+# Use unshallow to prevent error with git-merge-base: https://stackoverflow.com/a/78596539/22975246
+git fetch --unshallow target "${TARGET_BRANCH:?}" || git fetch target "${TARGET_BRANCH:?}"
 
 if [[ "${CI_MERGE_REQUEST_SOURCE_BRANCH_NAME}" ]]; then
     git remote add source "${CI_MERGE_REQUEST_SOURCE_PROJECT_URL}"
-    git fetch --unshallow source "${CI_MERGE_REQUEST_SOURCE_BRANCH_NAME}"
+    git fetch --unshallow source "${CI_MERGE_REQUEST_SOURCE_BRANCH_NAME}" || git fetch source "${CI_MERGE_REQUEST_SOURCE_BRANCH_NAME}"
 elif [[ "${CI_COMMIT_BRANCH}" ]]; then
-    git fetch origin "${CI_COMMIT_BRANCH:?}"
+    git fetch --unshallow origin "${CI_COMMIT_BRANCH:?}" || git fetch origin "${CI_COMMIT_BRANCH:?}"
 else
-    git fetch origin
+    git fetch --unshallow origin || git fetch origin
 fi
 
 BASE_VERSION=$(git merge-base "target/${TARGET_BRANCH:?}" "${VERSION:?}")