diff --git a/util/vm/build.py b/util/vm/build.py
index 6f8b521..dda4b93 100755
--- a/util/vm/build.py
+++ b/util/vm/build.py
@@ -765,7 +765,7 @@ def getMininetVersion( vm ):
 
 
 def bootAndRunTests( image, tests=None, pre='', post='', prompt=Prompt,
-                     memory=1024 ):
+                     memory=1024, outputFile=None ):
     """Boot and test VM
        tests: list of tests to run
        pre: command line to run in VM before tests
@@ -802,6 +802,9 @@ def bootAndRunTests( image, tests=None, pre='', post='', prompt=Prompt,
     vm.sendline( 'sudo shutdown -h now ' )
     log( '* Waiting for shutdown' )
     vm.wait()
+    if outputFile:
+        log( '* Saving temporary image to %s' % outputFile )
+        convert( cow, outputFile )
     log( '* Removing temporary dir', tmpdir )
     srun( 'rm -rf ' + tmpdir )
     elapsed = time() - bootTestStart
@@ -868,6 +871,8 @@ def parseArgs():
                          help='VM flavor(s) to build (e.g. raring32server)' )
     parser.add_argument( '-z', '--zip', action='store_true',
                          help='archive .ovf and .vmdk into .zip file' )
+    parser.add_argument( '-o', '--out', 
+                         help='output file for test image (vmdk)' )
     args = parser.parse_args()
     if args.depend:
         depend()
@@ -900,7 +905,8 @@ def parseArgs():
             exit( 1 )
     for image in args.image:
         bootAndRunTests( image, tests=args.test, pre=args.run,
-                         post=args.post, memory=args.memory)
+                         post=args.post, memory=args.memory, 
+                         outputFile=args.out )
     if not ( args.depend or args.list or args.clean or args.flavor
              or args.image ):
         parser.print_help()