diff --git a/installer/roles/local_docker/tasks/standalone.yml b/installer/roles/local_docker/tasks/standalone.yml
index 44d554ed54..ad7a064921 100644
--- a/installer/roles/local_docker/tasks/standalone.yml
+++ b/installer/roles/local_docker/tasks/standalone.yml
@@ -82,9 +82,11 @@
     state: started
     restart_policy: unless-stopped
     image: "{{ awx_web_docker_actual_image }}"
-    volumes:
-      - "{{ project_data_dir + ':/var/lib/awx/projects:z' if project_data_dir is defined else [] }}"
-      - "{{ ca_trust_dir + ':/etc/pki/ca-trust/source/anchors:ro' if ca_trust_dir is defined else [] }}"
+    volumes: >
+      {{
+        ([project_data_dir + ':/var/lib/awx/projects:z'] if project_data_dir is defined else [])
+        + ([ca_trust_dir + ':/etc/pki/ca-trust/source/anchors:ro'] if ca_trust_dir is defined else [])
+      }}
     user: root
     ports:
       - "{{ host_port }}:8052"
@@ -125,8 +127,8 @@
     image: "{{ awx_task_docker_actual_image }}"
     volumes: >
       {{
-        [project_data_dir + ':/var/lib/awx/projects:z'] if project_data_dir is defined else []
-        + [ca_trust_dir + ':/etc/pki/ca-trust/source/anchors:ro'] if ca_trust_dir is defined else []
+        ([project_data_dir + ':/var/lib/awx/projects:z'] if project_data_dir is defined else [])
+        + ([ca_trust_dir + ':/etc/pki/ca-trust/source/anchors:ro'] if ca_trust_dir is defined else [])
       }}
     links: "{{ awx_task_container_links|list }}"
     user: root