diff --git a/Modules/_iomodule.h b/Modules/_iomodule.h
index a2f24130579..a44f1277ba4 100644
--- a/Modules/_iomodule.h
+++ b/Modules/_iomodule.h
@@ -64,7 +64,7 @@ typedef struct {
     PyObject *filename; /* Not used, but part of the IOError object */
     Py_ssize_t written;
 } PyBlockingIOErrorObject;
-PyObject *PyExc_BlockingIOError;
+PyAPI_DATA(PyObject *) PyExc_BlockingIOError;
 
 /*
  * Offset type for positioning.