diff --git a/src/unix/bsd/mod.rs b/src/unix/bsd/mod.rs
index 047fc5afe154bf20fb8adee8ae171da14ae3f3ce..14c4eb92aedd810373932b7ee5d3dc98a44b7c25 100644
--- a/src/unix/bsd/mod.rs
+++ b/src/unix/bsd/mod.rs
@@ -298,6 +298,8 @@ pub const LOG_AUTHPRIV: ::c_int = 10 << 3;
 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 e5c1dd771ef37a391ba999384e078f2166aa9067..94868d8a434a97b4a947c0ca83219ed0254609eb 100644
--- a/src/unix/notbsd/mod.rs
+++ b/src/unix/notbsd/mod.rs
@@ -650,6 +650,8 @@ pub const LOG_AUTHPRIV: ::c_int = 10 << 3;
 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;