diff --git a/common/fs/loopbackvolume.py b/common/fs/loopbackvolume.py
index d7a6b6b..6bf74c8 100644
--- a/common/fs/loopbackvolume.py
+++ b/common/fs/loopbackvolume.py
@@ -17,6 +17,8 @@ class LoopbackVolume(Volume):
 	          {'name': 'delete', 'src': 'detached', 'dst': 'deleted'},
 	          ]
 
+	extension = 'raw'
+
 	def create(self, image_path):
 		self.fsm.create(image_path=image_path)
 
diff --git a/providers/virtualbox/volume.py b/providers/virtualbox/volume.py
index be47c47..2744233 100644
--- a/providers/virtualbox/volume.py
+++ b/providers/virtualbox/volume.py
@@ -6,6 +6,8 @@ from common.fs import get_partitions
 
 class VirtualBoxVolume(LoopbackVolume):
 
+	extension = 'vdi'
+
 	def _before_create(self, e):
 		self.image_path = e.image_path
 		log_check_call(['/usr/bin/qemu-img', 'create', '-f', 'vdi', self.image_path, str(self.size) + 'M'])