diff --git a/tests/Dockerfile.ubuntu-12 b/tests/Dockerfile.ubuntu-12
index 8e326d5..35ca2c6 100644
--- a/tests/Dockerfile.ubuntu-12
+++ b/tests/Dockerfile.ubuntu-12
@@ -1,5 +1,8 @@
 FROM ubuntu:12.04
 
+# Add `apt-add-repository`.
+sudo apt-get install python-software-properties
+
 # Install Ansible
 RUN apt-get install -y software-properties-common git
 RUN apt-add-repository -y ppa:ansible/ansible