diff --git a/src/proto/fileio.pro b/src/proto/fileio.pro
index 748bf4c..30582d4 100644
--- a/src/proto/fileio.pro
+++ b/src/proto/fileio.pro
@@ -1,6 +1,7 @@
 /* fileio.c */
 void filemess(buf_T *buf, char_u *name, char_u *s, int attr);
 int readfile(char_u *fname, char_u *sfname, linenr_T from, linenr_T lines_to_skip, linenr_T lines_to_read, exarg_T *eap, int flags);
+int is_dev_fd_file(char_u *fname);
 int prep_exarg(exarg_T *eap, buf_T *buf);
 void set_file_options(int set_options, exarg_T *eap);
 void set_forced_fenc(exarg_T *eap);