Index: Lib/io.py
===================================================================
--- Lib/io.py	(revision 67306)
+++ Lib/io.py	(working copy)
@@ -218,7 +218,7 @@
                  (reading and "r" or "") +
                  (writing and "w" or "") +
                  (appending and "a" or "") +
-                 (updating and "+" or ""),
+                 (updating and "+" or "") + "b",
                  closefd)
     if buffering is None:
         buffering = -1
Index: Modules/_fileio.c
===================================================================
--- Modules/_fileio.c	(revision 67306)
+++ Modules/_fileio.c	(working copy)
@@ -214,6 +214,8 @@
 			self->readable = self->writable = 1;
 			plus = 1;
 			break;
+                case 'b':
+			break;
 		default:
 			PyErr_Format(PyExc_ValueError,
 				     "invalid mode: %.200s", mode);
@@ -682,12 +684,12 @@
 {
 	if (self->readable) {
 		if (self->writable)
-			return "r+";
+			return "rb+";
 		else
-			return "r";
+			return "rb";
 	}
 	else
-		return "w";
+		return "wb";
 }
 
 static PyObject *