diff --git a/Include/cpython/pythread.h b/Include/cpython/pythread.h
index ce4ec8f65b15ea..cd2aab72d52df3 100644
--- a/Include/cpython/pythread.h
+++ b/Include/cpython/pythread.h
@@ -4,13 +4,6 @@
 
 #define PYTHREAD_INVALID_THREAD_ID ((unsigned long)-1)
 
-#ifdef HAVE_FORK
-/* Private function to reinitialize a lock at fork in the child process.
-   Reset the lock to the unlocked state.
-   Return 0 on success, return -1 on error. */
-PyAPI_FUNC(int) _PyThread_at_fork_reinit(PyThread_type_lock *lock);
-#endif  /* HAVE_FORK */
-
 #ifdef HAVE_PTHREAD_H
     /* Darwin needs pthread.h to know type name the pthread_key_t. */
 #   include <pthread.h>
diff --git a/Include/internal/pycore_pythread.h b/Include/internal/pycore_pythread.h
index 44846c0fc4b4c3..5ec2abda91e86b 100644
--- a/Include/internal/pycore_pythread.h
+++ b/Include/internal/pycore_pythread.h
@@ -75,6 +75,14 @@ struct _pythread_runtime_state {
 };
 
 
+#ifdef HAVE_FORK
+/* Private function to reinitialize a lock at fork in the child process.
+   Reset the lock to the unlocked state.
+   Return 0 on success, return -1 on error. */
+extern int _PyThread_at_fork_reinit(PyThread_type_lock *lock);
+#endif  /* HAVE_FORK */
+
+
 #ifdef __cplusplus
 }
 #endif