diff --git a/include/bio.h b/include/bio.h
index fda598a..600f094 100644
--- a/include/bio.h
+++ b/include/bio.h
@@ -55,6 +55,7 @@
 	(bp)->fid
 
 int	Bbuffered(Biobuf*);
+Biobuf*	Bfdopen(int, int);
 int	Bfildes(Biobuf*);
 int	Bflush(Biobuf*);
 int	Bgetc(Biobuf*);