diff --git a/lib/client/gnt_group.py b/lib/client/gnt_group.py
index 74a6d397e8bb0592785a3a9b1d4bb49493248732..538c1cbe9fa4cf6ba6fd77844542d86e769bb459 100644
--- a/lib/client/gnt_group.py
+++ b/lib/client/gnt_group.py
@@ -212,6 +212,7 @@ def EvacuateGroup(opts, args):
 
   return rcode
 
+
 commands = {
   "add": (
     AddGroup, ARGS_ONE_GROUP, [DRY_RUN_OPT, ALLOC_POLICY_OPT, NODE_PARAMS_OPT],
@@ -243,7 +244,8 @@ commands = {
   "evacuate": (
     EvacuateGroup, [ArgGroup(min=1, max=1)],
     [TO_GROUP_OPT, IALLOCATOR_OPT, EARLY_RELEASE_OPT],
-    "-I <iallocator> [--to <group>]", "Evacuate all instances within a group"),
+    "[-I <iallocator>] [--to <group>]",
+    "Evacuate all instances within a group"),
   "list-tags": (
     ListTags, ARGS_ONE_GROUP, [PRIORITY_OPT],
     "<instance_name>", "List the tags of the given instance"),
diff --git a/lib/cmdlib.py b/lib/cmdlib.py
index eee643e1e92d776da38853ca2c01ab3f12d3c22c..8141043f996dec23442b1f64a704eb2217887ff9 100644
--- a/lib/cmdlib.py
+++ b/lib/cmdlib.py
@@ -12191,7 +12191,8 @@ class LUGroupEvacuate(LogicalUnit):
                            if group_uuid != self.group_uuid]
 
       if not self.target_uuids:
-        raise errors.OpExecError("There are no possible target groups")
+        raise errors.OpPrereqError("There are no possible target groups",
+                                   errors.ECODE_INVAL)
 
   def BuildHooksEnv(self):
     """Build hooks env.