diff --git a/wsme/rest/args.py b/wsme/rest/args.py
index 7769e18..0bdc7d0 100644
--- a/wsme/rest/args.py
+++ b/wsme/rest/args.py
@@ -9,6 +9,7 @@ from wsme.exc import ClientSideError, UnknownArgument
 from wsme.types import iscomplex, list_attributes, Unset
 from wsme.types import UserType, ArrayType, DictType, File
 from wsme.utils import parse_isodate, parse_isotime, parse_isodatetime
+import wsme.runtime
 
 ARRAY_MAX_SIZE = 1000
 
@@ -273,8 +274,10 @@ def get_args(funcdef, args, kwargs, params, form, body, mimetype):
         (from_params, from_form_params, from_body)
     )
 
-    return combine_args(
+    args, kwargs = combine_args(
         funcdef,
         (from_args, from_params_and_body),
         allow_override=True
     )
+    wsme.runtime.check_arguments(funcdef, args, kwargs)
+    return args, kwargs
diff --git a/wsme/rest/protocol.py b/wsme/rest/protocol.py
index 8e8c4ac..85c76fd 100644
--- a/wsme/rest/protocol.py
+++ b/wsme/rest/protocol.py
@@ -6,6 +6,7 @@ from wsme.protocol import CallContext, Protocol
 
 import wsme.rest
 import wsme.rest.args
+import wsme.runtime
 
 log = logging.getLogger(__name__)
 
@@ -120,7 +121,7 @@ class RestProtocol(Protocol):
             (wsme.rest.args.args_from_params(funcdef, request.params),
              wsme.rest.args.args_from_body(funcdef, body, context.inmime))
         )
-        assert len(args) == 0
+        wsme.runtime.check_arguments(funcdef, args, kwargs)
         return kwargs
 
     def encode_result(self, context, result):
diff --git a/wsme/root.py b/wsme/root.py
index 0ce9431..157704c 100644
--- a/wsme/root.py
+++ b/wsme/root.py
@@ -7,7 +7,7 @@ import six
 
 import webob
 
-from wsme.exc import ClientSideError, MissingArgument, UnknownFunction
+from wsme.exc import ClientSideError, UnknownFunction
 from wsme.protocol import getprotocol
 from wsme.rest import scan_api
 from wsme import spore
@@ -180,10 +180,6 @@ class WSRoot(object):
             kw = protocol.read_arguments(context)
             args = list(args)
 
-            for arg in context.funcdef.arguments:
-                if arg.mandatory and arg.name not in kw:
-                    raise MissingArgument(arg.name)
-
             txn = self.begin()
             try:
                 result = context.func(*args, **kw)
diff --git a/wsme/runtime.py b/wsme/runtime.py
new file mode 100644
index 0000000..e114d13
--- /dev/null
+++ b/wsme/runtime.py
@@ -0,0 +1,9 @@
+from wsme.exc import MissingArgument
+
+
+def check_arguments(funcdef, args, kw):
+    """Check if some arguments are missing"""
+    assert len(args) == 0
+    for arg in funcdef.arguments:
+        if arg.mandatory and arg.name not in kw:
+            raise MissingArgument(arg.name)
diff --git a/wsmeext/cornice.py b/wsmeext/cornice.py
index 53a4d4f..3e8b469 100644
--- a/wsmeext/cornice.py
+++ b/wsmeext/cornice.py
@@ -19,6 +19,7 @@ from __future__ import absolute_import
 import wsme
 from wsme.rest import json as restjson
 from wsme.rest import xml as restxml
+import wsme.runtime
 import functools
 
 from wsme.rest.args import (
@@ -76,6 +77,7 @@ def signature(*args, **kwargs):
                 (args_from_params(funcdef, request.params),
                  args_from_body(funcdef, request.body, request.content_type))
             )
+            wsme.runtime.check_arguments(funcdef, args, kwargs)
             request.override_renderer = 'wsme' + get_outputformat(request)
             if funcdef.pass_request:
                 kwargs[funcdef.pass_request] = request
diff --git a/wsmeext/extdirect/protocol.py b/wsmeext/extdirect/protocol.py
index c510f2c..4cd7986 100644
--- a/wsmeext/extdirect/protocol.py
+++ b/wsmeext/extdirect/protocol.py
@@ -363,9 +363,11 @@ class ExtDirectProtocol(Protocol):
 
     def read_arguments(self, context):
         if isinstance(context, ExtCallContext):
-            return self.read_std_arguments(context)
+            kwargs = self.read_std_arguments(context)
         elif isinstance(context, FormExtCallContext):
-            return self.read_form_arguments(context)
+            kwargs = self.read_form_arguments(context)
+        wsme.runtime.check_arguments(context.funcdef, (), kwargs)
+        return kwargs
 
     def encode_result(self, context, result):
         return json.dumps({
diff --git a/wsmeext/soap/protocol.py b/wsmeext/soap/protocol.py
index ca65a81..599aea3 100644
--- a/wsmeext/soap/protocol.py
+++ b/wsmeext/soap/protocol.py
@@ -25,6 +25,8 @@ except ImportError:
 from wsme.protocol import CallContext, Protocol, expose
 
 import wsme.types
+import wsme.runtime
+
 from wsme import exc
 from wsme.utils import parse_isodate, parse_isotime, parse_isodatetime
 
@@ -384,7 +386,7 @@ class SoapProtocol(Protocol):
                 'type': self.typenamespace,
             })
             kw[name] = value
-
+        wsme.runtime.check_arguments(context.funcdef, (), kw)
         return kw
 
     def soap_response(self, path, funcdef, result):