diff --git a/src/unix/bsd/mod.rs b/src/unix/bsd/mod.rs
index 047fc5a..14c4eb9 100644
--- a/src/unix/bsd/mod.rs
+++ b/src/unix/bsd/mod.rs
@@ -298,6 +298,8 @@
 pub const LOG_FTP: ::c_int = 11 << 3;
 pub const LOG_PERROR: ::c_int = 0x20;
 
+pub const PIPE_BUF: usize = 512;
+
 f! {
     pub fn FD_CLR(fd: ::c_int, set: *mut fd_set) -> () {
         let bits = mem::size_of_val(&(*set).fds_bits[0]) * 8;
diff --git a/src/unix/notbsd/mod.rs b/src/unix/notbsd/mod.rs
index e5c1dd7..94868d8 100644
--- a/src/unix/notbsd/mod.rs
+++ b/src/unix/notbsd/mod.rs
@@ -650,6 +650,8 @@
 pub const LOG_FTP: ::c_int = 11 << 3;
 pub const LOG_PERROR: ::c_int = 0x20;
 
+pub const PIPE_BUF: usize = 4096;
+
 f! {
     pub fn FD_CLR(fd: ::c_int, set: *mut fd_set) -> () {
         let fd = fd as usize;