diff --git a/src/unix/bsd/apple/mod.rs b/src/unix/bsd/apple/mod.rs
index 0eaaced03ec2a..9f49ebabd5fad 100644
--- a/src/unix/bsd/apple/mod.rs
+++ b/src/unix/bsd/apple/mod.rs
@@ -860,6 +860,8 @@ pub const SO_RCVTIMEO: ::c_int = 0x1006;
 pub const SO_ERROR: ::c_int = 0x1007;
 pub const SO_TYPE: ::c_int = 0x1008;
 
+pub const MSG_PEEK: ::c_int = 0x2;
+
 pub const IFF_LOOPBACK: ::c_int = 0x8;
 
 pub const SHUT_RD: ::c_int = 0;
diff --git a/src/unix/bsd/freebsdlike/dragonfly/mod.rs b/src/unix/bsd/freebsdlike/dragonfly/mod.rs
index ddb71502921bb..c5664ac23ca3f 100644
--- a/src/unix/bsd/freebsdlike/dragonfly/mod.rs
+++ b/src/unix/bsd/freebsdlike/dragonfly/mod.rs
@@ -344,6 +344,7 @@ pub const NOTE_TRACK: ::uint32_t = 0x00000001;
 pub const NOTE_TRACKERR: ::uint32_t = 0x00000002;
 pub const NOTE_CHILD: ::uint32_t = 0x00000004;
 
+pub const MSG_PEEK: ::c_int = 0x2;
 pub const MSG_NOSIGNAL: ::c_int = 0x400;
 
 pub const EMPTY: ::c_short = 0;
diff --git a/src/unix/bsd/freebsdlike/freebsd/mod.rs b/src/unix/bsd/freebsdlike/freebsd/mod.rs
index ba56d1e13e781..bc23fd8851c8d 100644
--- a/src/unix/bsd/freebsdlike/freebsd/mod.rs
+++ b/src/unix/bsd/freebsdlike/freebsd/mod.rs
@@ -331,6 +331,7 @@ pub const USER_MAXID: ::c_int = 21;
 #[doc(hidden)]
 pub const CTL_P1003_1B_MAXID: ::c_int = 26;
 
+pub const MSG_PEEK: ::c_int = 0x2;
 pub const MSG_NOSIGNAL: ::c_int = 0x20000;
 
 pub const EMPTY: ::c_short = 0;
diff --git a/src/unix/bsd/netbsdlike/mod.rs b/src/unix/bsd/netbsdlike/mod.rs
index 5fb527d44bf0d..e8c82883d2bb0 100644
--- a/src/unix/bsd/netbsdlike/mod.rs
+++ b/src/unix/bsd/netbsdlike/mod.rs
@@ -392,6 +392,7 @@ pub const SO_RCVLOWAT: ::c_int = 0x1004;
 pub const SO_ERROR: ::c_int = 0x1007;
 pub const SO_TYPE: ::c_int = 0x1008;
 
+pub const MSG_PEEK: ::c_int = 0x2;
 pub const MSG_NOSIGNAL: ::c_int = 0x400;
 
 pub const IFF_LOOPBACK: ::c_int = 0x8;
diff --git a/src/unix/haiku/mod.rs b/src/unix/haiku/mod.rs
index ab53e6c788c68..313f7da2dbc38 100644
--- a/src/unix/haiku/mod.rs
+++ b/src/unix/haiku/mod.rs
@@ -556,6 +556,7 @@ pub const IPV6_V6ONLY: ::c_int = 30;
 
 pub const SO_DEBUG: ::c_int = 0x00000004;
 
+pub const MSG_PEEK: ::c_int = 0x2;
 pub const MSG_NOSIGNAL: ::c_int = 0x0800;
 
 pub const SHUT_RD: ::c_int = 0;
diff --git a/src/unix/notbsd/mod.rs b/src/unix/notbsd/mod.rs
index 39ad6d79c0d76..e7beb7b1814ed 100644
--- a/src/unix/notbsd/mod.rs
+++ b/src/unix/notbsd/mod.rs
@@ -468,6 +468,7 @@ pub const IPV6_V6ONLY: ::c_int = 26;
 
 pub const SO_DEBUG: ::c_int = 1;
 
+pub const MSG_PEEK: ::c_int = 0x2;
 pub const MSG_NOSIGNAL: ::c_int = 0x4000;
 
 pub const SHUT_RD: ::c_int = 0;