diff --git a/Modules/_io/_iomodule.c b/Modules/_io/_iomodule.c
index 0d8a638..cba4732 100644
--- a/Modules/_io/_iomodule.c
+++ b/Modules/_io/_iomodule.c
@@ -324,7 +324,7 @@
     if (universal) {
         if (creating || writing || appending || updating) {
             PyErr_SetString(PyExc_ValueError,
-                            "mode U cannot be combined with x', 'w', 'a', or '+'");
+                            "mode U cannot be combined with 'x', 'w', 'a', or '+'");
             goto error;
         }
         if (PyErr_WarnEx(PyExc_DeprecationWarning,