diff --git a/Include/cpython/bytesobject.h b/Include/cpython/bytesobject.h
index 816823716e9..41537210b74 100644
--- a/Include/cpython/bytesobject.h
+++ b/Include/cpython/bytesobject.h
@@ -31,3 +31,7 @@ static inline Py_ssize_t PyBytes_GET_SIZE(PyObject *op) {
     return Py_SIZE(self);
 }
 #define PyBytes_GET_SIZE(self) PyBytes_GET_SIZE(_PyObject_CAST(self))
+
+/* _PyBytes_Join(sep, x) is like sep.join(x).  sep must be PyBytesObject*,
+   x must be an iterable object. */
+PyAPI_FUNC(PyObject*) _PyBytes_Join(PyObject *sep, PyObject *x);
diff --git a/Include/internal/pycore_bytesobject.h b/Include/internal/pycore_bytesobject.h
index 94d421a9eb7..300e7f4896a 100644
--- a/Include/internal/pycore_bytesobject.h
+++ b/Include/internal/pycore_bytesobject.h
@@ -23,10 +23,6 @@ extern PyObject* _PyBytes_FromHex(
 PyAPI_FUNC(PyObject*) _PyBytes_DecodeEscape(const char *, Py_ssize_t,
                                             const char *, const char **);
 
-/* _PyBytes_Join(sep, x) is like sep.join(x).  sep must be PyBytesObject*,
-   x must be an iterable object. */
-extern PyObject* _PyBytes_Join(PyObject *sep, PyObject *x);
-
 
 // Substring Search.
 //
diff --git a/Misc/NEWS.d/next/C API/2024-07-21-17-40-07.gh-issue-121489.SUMFCr.rst b/Misc/NEWS.d/next/C API/2024-07-21-17-40-07.gh-issue-121489.SUMFCr.rst
new file mode 100644
index 00000000000..8c18a49c05d
--- /dev/null
+++ b/Misc/NEWS.d/next/C API/2024-07-21-17-40-07.gh-issue-121489.SUMFCr.rst	
@@ -0,0 +1 @@
+Export private :c:func:`!_PyBytes_Join` again.
diff --git a/Modules/_io/bufferedio.c b/Modules/_io/bufferedio.c
index aa52711941d..e45323c93a1 100644
--- a/Modules/_io/bufferedio.c
+++ b/Modules/_io/bufferedio.c
@@ -8,7 +8,6 @@
 */
 
 #include "Python.h"
-#include "pycore_bytesobject.h"         // _PyBytes_Join()
 #include "pycore_call.h"                // _PyObject_CallNoArgs()
 #include "pycore_object.h"              // _PyObject_GC_UNTRACK()
 #include "pycore_pyerrors.h"            // _Py_FatalErrorFormat()