diff --git a/.gitlab-ci-checkcommit.sh b/.gitlab-ci-checkcommit.sh
index d76baf7..c1c524d 100755
--- a/.gitlab-ci-checkcommit.sh
+++ b/.gitlab-ci-checkcommit.sh
@@ -38,13 +38,13 @@
 
 	commit_body=$(git show -s --pretty=%b "$h")
 
-	author=$(git show -s --format='%an <%ae>')
+	author=$(git show -s --format='%an <%ae>' "$h")
 	if findtag "$commit_body" "Signed-off-by" "$author"; then
 		echoerr "Author SoB tag is missing from commit $h"
 		exit 1
 	fi
 
-	committer=$(git show -s --format='%cn <%ce>')
+	committer=$(git show -s --format='%cn <%ce>' "$h")
 	if findtag "$commit_body" "Signed-off-by" "$committer"; then
 		echoerr "Committer SoB tag is missing from commit $h"
 		exit 1