diff --git a/defaults/main.yml b/defaults/main.yml
index 909d982..027618d 100644
--- a/defaults/main.yml
+++ b/defaults/main.yml
@@ -4,6 +4,12 @@
 # file path is not given.
 libvirt_vm_default_console_log_dir: "/var/log/libvirt-consoles/"
 
+# The default format for Libvirt volumes.
+libvirt_volume_default_format: qcow2
+
+# The default device for Libvirt volumes.
+libvirt_volume_default_device: disk
+
 # Path to cache downloaded images.
 libvirt_image_cache_path: "/tmp/"
 
diff --git a/tasks/autodetect.yml b/tasks/autodetect.yml
index 404ef7d..a29647c 100644
--- a/tasks/autodetect.yml
+++ b/tasks/autodetect.yml
@@ -40,6 +40,7 @@
         - name: Detect the QEMU emulator binary path
           shell: which qemu-system-{{ libvirt_vm_arch }}
           register: qemu_emulator_result
+          changed_when: false
 
         - name: Set a fact containing the QEMU emulator binary path
           set_fact:
diff --git a/tasks/main.yml b/tasks/main.yml
index 772b9a2..88ae3e8 100644
--- a/tasks/main.yml
+++ b/tasks/main.yml
@@ -1,7 +1,10 @@
 ---
 - include_tasks: autodetect.yml
-  # We need to know the engine and emulator if we're creating any new VMs.
-  when: libvirt_vms | rejectattr('state', 'eq', 'absent') | list
+  # We don't need to know the engine and emulator if we're not creating any new
+  # VMs.
+  when: >-
+    (libvirt_vms | selectattr('state', 'defined')
+       | selectattr('state', 'eq', 'absent') | list) != libvirt_vms
 
 - include_tasks: volumes.yml
   vars:
diff --git a/tasks/volumes.yml b/tasks/volumes.yml
index 1c49872..7422d5b 100644
--- a/tasks/volumes.yml
+++ b/tasks/volumes.yml
@@ -19,7 +19,7 @@
     {{ item.name }}
     {{ item.pool }}
     {{ item.capacity }}
-    {{ item.format | default('qcow2') }}
+    {{ item.format | default(libvirt_volume_default_format) }}
     {% if item.image is defined %}
     {{ libvirt_vm_image_cache_path }}/{{ item.image | basename }}
     {% endif %}
diff --git a/templates/vm.xml.j2 b/templates/vm.xml.j2
index 9aed95d..987c147 100644
--- a/templates/vm.xml.j2
+++ b/templates/vm.xml.j2
@@ -19,8 +19,8 @@
   <devices>
     <emulator>{{ libvirt_vm_emulator }}</emulator>
 {% for volume in volumes %}
-    <disk type='volume' device='{{ volume.device | default('disk') }}'>
-      <driver name='qemu' type='{{ volume.format }}'/>
+    <disk type='volume' device='{{ volume.device | default(libvirt_volume_default_device) }}'>
+      <driver name='qemu' type='{{ volume.format | default(libvirt_volume_default_format) }}'/>
       <source pool='{{ volume.pool }}' volume='{{ volume.name }}'/>
       <target dev='vd{{ 'abcdefghijklmnopqrstuvwxyz'[loop.index] }}'/>
     </disk>