diff --git a/Modules/_io/bufferedio.c b/Modules/_io/bufferedio.c
index 6b43161a73a610a..50769e419303fe9 100644
--- a/Modules/_io/bufferedio.c
+++ b/Modules/_io/bufferedio.c
@@ -1497,7 +1497,9 @@ buffered_iternext(PyObject *op)
         tp == state->PyBufferedRandom_Type)
     {
         /* Skip method call overhead for speed */
+        Py_BEGIN_CRITICAL_SECTION(self);
         line = _buffered_readline(self, -1);
+        Py_END_CRITICAL_SECTION();
     }
     else {
         line = PyObject_CallMethodNoArgs((PyObject *)self,