diff --git a/tests/docker-build.sh b/tests/docker-build.sh
index 272c59a..f47bec9 100755
--- a/tests/docker-build.sh
+++ b/tests/docker-build.sh
@@ -4,6 +4,7 @@
 # if condition becomes more difficult.
 
 set -eou pipefail
+set -x
 
 apt-get update
 apt-get -y -q upgrade