diff --git a/basis/unix/ffi/linux/linux.factor b/basis/unix/ffi/linux/linux.factor
index 94e42e224d..a28935feef 100644
--- a/basis/unix/ffi/linux/linux.factor
+++ b/basis/unix/ffi/linux/linux.factor
@@ -275,3 +275,5 @@ CONSTANT: SIGIO           29
 ALIAS:    SIGPOLL         SIGIO
 CONSTANT: SIGPWR          30
 CONSTANT: SIGSYS          31
+
+FUNCTION: ssize_t sendfile ( int out_fd, int in_fd, off_t* offset, size_t count ) ;
diff --git a/basis/unix/ffi/macosx/macosx.factor b/basis/unix/ffi/macosx/macosx.factor
index 10d67d997b..6e994fbe82 100644
--- a/basis/unix/ffi/macosx/macosx.factor
+++ b/basis/unix/ffi/macosx/macosx.factor
@@ -264,3 +264,11 @@ CONSTANT: SIGWINCH  28
 CONSTANT: SIGINFO   29
 CONSTANT: SIGUSR1   30
 CONSTANT: SIGUSR2   31
+
+STRUCT: sf_hdtr
+    { headers iovec* }
+    { hdr_cnt int }
+    { trailers iovec* }
+    { trl_cnt int } ;
+
+FUNCTION: int sendfile ( int fd, int s, off_t offset, off_t* len, sf_hdtr* hdtr, int flags ) ;