diff --git a/lib/libc/include/libc_private.h b/lib/libc/include/libc_private.h
index 71fc8df9009..e4bf4a6afd8 100644
--- a/lib/libc/include/libc_private.h
+++ b/lib/libc/include/libc_private.h
@@ -271,7 +271,7 @@ void _malloc_first_thread(void);
 /*
  * Function to clean up streams, called from abort() and exit().
  */
-void (*__cleanup)(void) __hidden;
+extern void (*__cleanup)(void) __hidden;
 
 /*
  * Get kern.osreldate to detect ABI revisions.  Explicitly