diff --git a/libc/stdio/stdio_ext.cpp b/libc/stdio/stdio_ext.cpp
index fea44f6..310076a 100644
--- a/libc/stdio/stdio_ext.cpp
+++ b/libc/stdio/stdio_ext.cpp
@@ -99,3 +99,7 @@
 int ferror_unlocked(FILE* fp) {
   return __sferror(fp);
 }
+
+int fileno_unlocked(FILE* fp) {
+  return __sfileno(fp);
+}