diff --git a/neat/globals/manager.py b/neat/globals/manager.py
index 1fb12ea..d6ab569 100644
--- a/neat/globals/manager.py
+++ b/neat/globals/manager.py
@@ -92,9 +92,8 @@ ERRORS = {
          'specified in the configuration file',
     405: 'Method not allowed: the request is made with ' +
          'a method other than the only supported PUT',
-    422: 'Unprocessable entity: one or more VMs could not ' +
-         'be found using the list of UUIDs specified in ' +
-         'the vm_uuids parameter'}
+    412: 'Precondition failed: some VMs possibly have been in ' +
+         'migration when the request has been sent - retry'}
 
 
 @contract
@@ -136,9 +135,13 @@ def validate_params(user, password, params):
         return False
     if 'reason' not in params or \
        params['reason'] == 1 and 'vm_uuids' not in params or \
-       params['reason'] == 0 and 'host' not in params:
+       params['reason'] == 0 and 'host' not in params or \
+       'time' not in params:
         raise_error(400)
         return False
+    if params['time'] + 5 < time.time():
+        raise_error(412)
+        return False
     log.debug('Request parameters validated')
     return True
 
@@ -176,6 +179,8 @@ def get_params(request):
      :rtype: dict(str: *)
     """
     params = dict(request.forms)
+    if 'time' in params:
+        params['time'] = float(params['time'])
     if 'reason' in params:
         params['reason'] = int(params['reason'])
     if 'vm_uuids' in params:
diff --git a/tests/globals/test_manager.py b/tests/globals/test_manager.py
index 7614f65..843c861 100644
--- a/tests/globals/test_manager.py
+++ b/tests/globals/test_manager.py
@@ -18,6 +18,7 @@ from pyqcy import *
 import bottle
 from hashlib import sha1
 from novaclient.v1_1 import client
+import time
 
 import neat.globals.manager as manager
 import neat.common as common
@@ -29,7 +30,7 @@ logging.disable(logging.CRITICAL)
 class GlobalManager(TestCase):
 
     def test_raise_error(self):
-        for error_code in [400, 401, 403, 405, 422]:
+        for error_code in [400, 401, 403, 405, 412]:
             try:
                 manager.raise_error(error_code)
             except bottle.HTTPResponse as e:
@@ -80,6 +81,7 @@ class GlobalManager(TestCase):
                 sha1('test2').hexdigest(),
                 {'username': sha1('test1').hexdigest(),
                  'password': sha1('test2').hexdigest(),
+                 'time': time.time(),
                  'reason': 1,
                  'vm_uuids': ['qwe', 'asd']})
 
@@ -88,27 +90,63 @@ class GlobalManager(TestCase):
                 sha1('test2').hexdigest(),
                 {'username': sha1('test1').hexdigest(),
                  'password': sha1('test2').hexdigest(),
+                 'time': time.time(),
                  'reason': 0,
                  'host': 'test'})
 
         with MockTransaction:
-            expect(manager).raise_error(400).exactly(5).times()
-            manager.validate_params('test', 'test', {'username': 'test',
-                                                     'password': 'test'})
+            expect(manager).raise_error(400).exactly(6).times()
             manager.validate_params('test', 'test', {'username': 'test',
                                                      'password': 'test',
+                                                     'time': time.time()})
+            manager.validate_params('test', 'test', {'username': 'test',
+                                                     'password': 'test',
+                                                     'time': time.time(),
                                                      'reason': 1})
             manager.validate_params('test', 'test', {'username': 'test',
                                                      'password': 'test',
+                                                     'time': time.time(),
                                                      'reason': 0})
             manager.validate_params('test', 'test', {'username': 'test',
                                                      'password': 'test',
+                                                     'time': time.time(),
                                                      'reason': 1,
                                                      'host': 'test'})
             manager.validate_params('test', 'test', {'username': 'test',
                                                      'password': 'test',
+                                                     'time': time.time(),
                                                      'reason': 0,
                                                      'vm_uuids': []})
+            manager.validate_params('test', 'test', {'username': 'test',
+                                                     'password': 'test',
+                                                     'reason': 0,
+                                                     'vm_uuids': []})
+
+        with MockTransaction:
+            expect(manager).raise_error(412).exactly(2).times()
+            manager.validate_params('test', 'test', {'username': 'test',
+                                                     'password': 'test',
+                                                     'time': 1.,
+                                                     'reason': 0,
+                                                     'host': 'test'})
+            manager.validate_params('test', 'test', {'username': 'test',
+                                                     'password': 'test',
+                                                     'time': time.time() - 6,
+                                                     'reason': 0,
+                                                     'host': 'test'})
+            assert manager.validate_params('test', 'test', 
+                                           {'username': 'test',
+                                            'password': 'test',
+                                            'time': time.time(),
+                                            'reason': 0,
+                                            'host': 'test'})
+            assert manager.validate_params('test', 'test', 
+                                           {'username': 'test',
+                                            'password': 'test',
+                                            'time': time.time() - 4,
+                                            'reason': 0,
+                                            'host': 'test'})
+
 
     def test_start(self):
         with MockTransaction: