diff --git a/src/unix/mod.rs b/src/unix/mod.rs
index f645357be021e6c6a639b40881076231081928c5..c2a45ff8f7122aa6cc2d5d2cb1b1794f04fe55b5 100644
--- a/src/unix/mod.rs
+++ b/src/unix/mod.rs
@@ -742,6 +742,7 @@ extern {
     pub fn getservbyname(name: *const ::c_char,
                          proto: *const ::c_char) -> *mut servent;
     pub fn getprotobyname(name: *const ::c_char) -> *mut protoent;
+    pub fn getprotobynumber(proto: ::c_int) -> *mut protoent;
     pub fn chroot(name: *const ::c_char) -> ::c_int;
     #[cfg_attr(all(target_os = "macos", target_arch = "x86"),
                link_name = "usleep$UNIX2003")]