Index: Objects/fileobject.c
===================================================================
--- Objects/fileobject.c	(revision 66486)
+++ Objects/fileobject.c	(working copy)
@@ -305,10 +305,17 @@
 #endif
                 /* EINVAL is returned when an invalid filename or
                  * an invalid mode is supplied. */
-		if (errno == EINVAL)
-			PyErr_Format(PyExc_IOError,
-                                     "invalid filename: %s or mode: %s",
-				     name, mode);
+		if (errno == EINVAL) {
+			PyObject *v;
+			char message[100];
+			PyOS_snprintf(message, 100, 
+			    "invalid filename or mode '%.50s'", mode);
+			v = Py_BuildValue("(isO)", errno, message, f->f_name);
+			if (v != NULL) {
+				PyErr_SetObject(PyExc_IOError, v);
+				Py_DECREF(v);
+			}
+		}
 		else
 			PyErr_SetFromErrnoWithFilenameObject(PyExc_IOError, f->f_name);
 		f = NULL;
Index: Lib/test/test_file.py
===================================================================
--- Lib/test/test_file.py	(revision 66486)
+++ Lib/test/test_file.py	(working copy)
@@ -134,6 +134,16 @@
                 f.close()
                 self.fail('%r is an invalid file mode' % mode)
 
+        # Some invalid modes fail on Windows, but pass on Unix
+        # Issue3965: avoid a crash on Windows when filename is unicode
+        for name in (TESTFN, unicode(TESTFN), unicode(TESTFN + '\t')):
+            try:
+                f = open(name, "rr")
+            except IOError:
+                pass
+            else:
+                f.close()
+
     def testStdin(self):
         # This causes the interpreter to exit on OSF1 v5.1.
         if sys.platform != 'osf1V5':