diff --git a/fio.h b/fio.h
index 544916f..9eecba3 100644
--- a/fio.h
+++ b/fio.h
@@ -441,7 +441,7 @@
 extern int ioengine_load(struct thread_data *);
 extern int parse_dryrun(void);
 extern int fio_running_or_pending_io_threads(void);
-extern void fio_set_fd_nonblocking(int, const char *);
+extern int fio_set_fd_nonblocking(int, const char *);
 
 extern uintptr_t page_mask;
 extern uintptr_t page_size;