--- a/taskcluster/docker/diffoscope/get_and_diffoscope
+++ b/taskcluster/docker/diffoscope/get_and_diffoscope
@@ -45,28 +45,34 @@ case "$ORIG_URL" in
 	;;
 esac
 
 # Builds are 99% of the time differing in some small ways, so it's not
 # really useful to report a failure (at least not until we actually
 # care about the builds being 100% identical).
 POST=true
 
+fail() {
+	set +x
+	echo "TEST-UNEXPECTED-FAIL | Builds differ. See the diff.html or diff.txt artifact"
+	exit 1
+}
+
 for option; do
 	case "$option" in
 	--unpack)
 		CURDIR=$PWD
 		for dir in a b; do
 			# Need to run mach python from inside the gecko source.
 			# See bug #1533642.
 			(cd $GECKO_PATH && ./mach python toolkit/mozapps/installer/unpack.py --omnijar $OMNIJAR $CURDIR/$dir)
 		done
 		;;
 	--fail)
-		POST="exit 1"
+		POST="fail"
 		;;
 	*)
 		echo "Unsupported option: $option" >&2
 		exit 1
 	esac
 done
 
 if [ -n "$PRE_DIFF" ]; then