diff --git a/.gitlab-ci-checkcommit.sh b/.gitlab-ci-checkcommit.sh
index 9023410..fc8963a 100755
--- a/.gitlab-ci-checkcommit.sh
+++ b/.gitlab-ci-checkcommit.sh
@@ -1,9 +1,37 @@
 #! /usr/bin/env bash
 
+echoerr() {
+	printf "ERROR: %s\n" "$*" >&2
+}
+
 git fetch https://gitlab.freedesktop.org/drm-hwcomposer/drm-hwcomposer.git
 
-git diff -U0 --no-color FETCH_HEAD...HEAD -- | clang-format-diff-5.0 -p 1 -style=file > format-fixup.patch
-if [ -s format-fixup.patch ]; then
-	cat format-fixup.patch
-	exit 1
-fi
+git log --pretty='%h' FETCH_HEAD..HEAD | while read h; do
+	subject=$(git show -s --pretty='%s' "$h")
+	if [[ $subject != drm_hwcomposer:* ]]; then
+		echoerr "Invalid subject prefix: $subject"
+		exit 1
+	fi
+
+	commit_body=$(git show -s --pretty=%b "$h")
+
+	author=$(git show -s --format='%an <%ae>')
+	sob=$(echo "$commit_body" | grep "Signed-off-by: $author")
+	if [ -z "$sob" ] ; then
+		echoerr "Author SoB tag is missing from commit $h"
+		exit 1
+	fi
+
+	committer=$(git show -s --format='%cn <%ce>')
+	sob=$(echo "$commit_body" | grep "Signed-off-by: $committer")
+	if [ -z "$sob" ] ; then
+		echoerr "Committer SoB tag is missing from commit $h"
+		exit 1
+	fi
+
+	git show "$h" -- | clang-format-diff-5.0 -p 1 -style=file > format-fixup.patch
+	if [ -s  format-fixup.patch ]; then
+		cat format-fixup.patch >&2
+		exit 1
+	fi
+done
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index d0175f0..c97f4ff 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -12,5 +12,4 @@
   script: "./.gitlab-ci-checkcommit.sh"
   artifacts:
     when: on_failure
-    paths:
-      - format-fixup.patch
+    untracked: true