diff --git a/src/os/unix/ngx_files.h b/src/os/unix/ngx_files.h
index 2efd247..ccaf44a 100644
--- a/src/os/unix/ngx_files.h
+++ b/src/os/unix/ngx_files.h
@@ -264,7 +264,7 @@
 
 #define NGX_HAVE_READ_AHEAD      1
 
-#define ngx_read_ahead(fd, n)    posix_fadvise(fd, 0, 0, POSIX_FADV_SEQUENTIAL)
+ngx_int_t ngx_read_ahead(ngx_fd_t fd, size_t n);
 #define ngx_read_ahead_n         "posix_fadvise(POSIX_FADV_SEQUENTIAL)"
 
 #else