diff --git a/github/Github.UnitTest.py b/github/Github.UnitTest.py
index b36664f1..73d75064 100644
--- a/github/Github.UnitTest.py
+++ b/github/Github.UnitTest.py
@@ -7,9 +7,10 @@ class TestCase( unittest.TestCase ):
     def setUp( self ):
         unittest.TestCase.setUp( self )
 
-        self.g = Github( "login", "password" )
-
         self.requester = MockMockMock.Mock( "requester" )
+        self.debugFile = MockMockMock.Mock( "debugFile", self.requester )
+
+        self.g = Github( "login", "password", self.debugFile.object )
         self.g._Github__requester = self.requester.object
 
     def tearDown( self ):
@@ -109,4 +110,9 @@ class TestCase( unittest.TestCase ):
         self.requester.expect.dataRequest( "GET", "/repos/xxx/yyy/compare/foo...bar", None, None ).andReturn( { "gabu": "zomeuh" } )
         self.assertEqual( self.g.get_user().get_repo( "yyy" ).compare( "foo", "bar" ), { "gabu": "zomeuh" } )
 
+    def testDebugPrint( self ):
+        self.requester.expect.dataRequest( "GET", "/user", None, None ).andReturn( { "login": "xxx", "unknownAttribute": 42 } )
+        self.debugFile.expect.write( "Missing definition of attribute unknownAttribute in class AuthenticatedUser\n" )
+        self.g.get_user().location
+
 unittest.main()
diff --git a/github/Github.py b/github/Github.py
index db5f6e57..e6373d6e 100644
--- a/github/Github.py
+++ b/github/Github.py
@@ -2,8 +2,9 @@ from Requester import Requester
 from GithubObjects import *
 
 class Github:
-    def __init__( self, login, password ):
+    def __init__( self, login, password, debugFile = None ):
         self.__requester = Requester( login, password )
+        self.__debugFile = debugFile
 
     def _dataRequest( self, verb, url, parameters, data ):
         return self.__requester.dataRequest( verb, url, parameters, data )
@@ -29,3 +30,7 @@ class Github:
             for attributes
             in self._dataRequest( "GET", "/gists/public", None, None )
         ]
+
+    def _printDebug( self, *args ):
+        if self.__debugFile is not None:
+            self.__debugFile.write( " ".join( str( arg ) for arg in args ) + "\n" )
diff --git a/github/GithubObjects/GithubObject/GithubObject.py b/github/GithubObjects/GithubObject/GithubObject.py
index f8b56fb8..72464749 100644
--- a/github/GithubObjects/GithubObject/GithubObject.py
+++ b/github/GithubObjects/GithubObject/GithubObject.py
@@ -88,7 +88,7 @@ def GithubObject( className, *attributePolicies ):
                     attributeDefinition = GithubObject.__attributeDefinitions[ attributeName ]
                     self.__attributes[ attributeName ] = attributeDefinition.getValueFromRawValue( self, attributeValue )
                 except KeyError:
-                    pass
+                    self._github._printDebug( "Missing definition of attribute", attributeName, "in class", className )
 
         def _markAsCompleted( self ):
             for attributeName, attributeDefinition in GithubObject.__attributeDefinitions.iteritems():