diff --git a/Modules/_io/bufferedio.c b/Modules/_io/bufferedio.c
index b21ea71..c0c3acc 100644
--- a/Modules/_io/bufferedio.c
+++ b/Modules/_io/bufferedio.c
@@ -632,6 +632,8 @@
         return -1;
     }
 #ifdef WITH_THREAD
+    if (self->lock)
+        PyThread_free_lock(self->lock);
     self->lock = PyThread_allocate_lock();
     if (self->lock == NULL) {
         PyErr_SetString(PyExc_RuntimeError, "can't allocate read lock");