diff --git a/libc/include/stdio.h b/libc/include/stdio.h
index 1df4b54..fd653d9 100644
--- a/libc/include/stdio.h
+++ b/libc/include/stdio.h
@@ -270,6 +270,7 @@
 void clearerr_unlocked(FILE*);
 int feof_unlocked(FILE*);
 int ferror_unlocked(FILE*);
+int fileno_unlocked(FILE*);
 
 /*
  * Stdio function-access interface.