diff --git a/Lib/test/test_file.py b/Lib/test/test_file.py
index 7cfaef7..b93bdbd 100644
--- a/Lib/test/test_file.py
+++ b/Lib/test/test_file.py
@@ -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':
diff --git a/Misc/NEWS b/Misc/NEWS
index 80e524d..660e88a 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,9 @@
 Core and Builtins
 -----------------
 
+- Issue #3965: Fixed a crash on Windows when open() is given an invalid
+  filename or mode, and the filename is a unicode string.
+
 - Bug #3951: Py_USING_MEMORY_DEBUGGER should not be enabled by default.
 
 Library
diff --git a/Objects/fileobject.c b/Objects/fileobject.c
index a8e95a2..b2051d7 100644
--- a/Objects/fileobject.c
+++ b/Objects/fileobject.c
@@ -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 mode ('%.50s') or filename", 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;