diff --git a/lib/cmdlib.py b/lib/cmdlib.py
index 23ee2e922d946054747d1fc93eade987fd10dbe5..b667019da346d5af1014d479bc00899e2fc65ba2 100644
--- a/lib/cmdlib.py
+++ b/lib/cmdlib.py
@@ -8244,7 +8244,7 @@ def _CheckOSParams(lu, required, nodenames, osname, osparams):
 
   """
   nodenames = _FilterVmNodes(lu, nodenames)
-  result = lu.rpc.call_os_validate(required, nodenames, osname,
+  result = lu.rpc.call_os_validate(nodenames, required, osname,
                                    [constants.OS_VALIDATE_PARAMETERS],
                                    osparams)
   for node, nres in result.items():
diff --git a/lib/rpc.py b/lib/rpc.py
index 7d75a58d5010c20c6a05645e14b17de518e2e1cb..61dbe88907a7973b7d4bc562af801620f81fb033 100644
--- a/lib/rpc.py
+++ b/lib/rpc.py
@@ -1240,7 +1240,7 @@ class RpcRunner(object):
     return result
 
   @_RpcTimeout(_TMO_FAST)
-  def call_os_validate(self, required, nodes, name, checks, params):
+  def call_os_validate(self, nodes, required, name, checks, params):
     """Run a validation routine for a given OS.
 
     This is a multi-node call.