diff --git a/src/fuchsia/mod.rs b/src/fuchsia/mod.rs
index 6b121854138e9..3e922e766cba4 100644
--- a/src/fuchsia/mod.rs
+++ b/src/fuchsia/mod.rs
@@ -3271,7 +3271,7 @@ f! {
             as ::c_uint
     }
 
-    pub fn CMSG_LEN(len: ::c_uint) -> ::c_uint {
+    pub {const} fn CMSG_LEN(len: ::c_uint) -> ::c_uint {
         (CMSG_ALIGN(::mem::size_of::<cmsghdr>()) + len as ::size_t) as ::c_uint
     }
 }
diff --git a/src/unix/aix/mod.rs b/src/unix/aix/mod.rs
index ffe3f18284d72..325d7d654fd7e 100644
--- a/src/unix/aix/mod.rs
+++ b/src/unix/aix/mod.rs
@@ -2551,7 +2551,7 @@ f! {
         (cmsg as *mut ::c_uchar).offset(::mem::size_of::<::cmsghdr>() as isize)
     }
 
-    pub fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
+    pub {const} fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
         ::mem::size_of::<::cmsghdr>() as ::c_uint + length
     }
 
diff --git a/src/unix/bsd/apple/mod.rs b/src/unix/bsd/apple/mod.rs
index 66f03f67f653c..4b6ce9b4c3634 100644
--- a/src/unix/bsd/apple/mod.rs
+++ b/src/unix/bsd/apple/mod.rs
@@ -5107,7 +5107,7 @@ f! {
             as ::c_uint
     }
 
-    pub fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
+    pub {const} fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
         (__DARWIN_ALIGN32(::mem::size_of::<::cmsghdr>()) + length as usize)
             as ::c_uint
     }
diff --git a/src/unix/bsd/freebsdlike/dragonfly/mod.rs b/src/unix/bsd/freebsdlike/dragonfly/mod.rs
index d323a43540b19..7d01e3e0d0374 100644
--- a/src/unix/bsd/freebsdlike/dragonfly/mod.rs
+++ b/src/unix/bsd/freebsdlike/dragonfly/mod.rs
@@ -1534,7 +1534,7 @@ f! {
             .offset(_CMSG_ALIGN(::mem::size_of::<::cmsghdr>()) as isize)
     }
 
-    pub fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
+    pub {const} fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
         (_CMSG_ALIGN(::mem::size_of::<::cmsghdr>()) + length as usize)
             as ::c_uint
     }
diff --git a/src/unix/bsd/freebsdlike/freebsd/mod.rs b/src/unix/bsd/freebsdlike/freebsd/mod.rs
index 6db9fa2c74e4b..633d1dac39c5c 100644
--- a/src/unix/bsd/freebsdlike/freebsd/mod.rs
+++ b/src/unix/bsd/freebsdlike/freebsd/mod.rs
@@ -4717,7 +4717,7 @@ f! {
             .offset(_ALIGN(::mem::size_of::<::cmsghdr>()) as isize)
     }
 
-    pub fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
+    pub {const} fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
         _ALIGN(::mem::size_of::<::cmsghdr>()) as ::c_uint + length
     }
 
diff --git a/src/unix/bsd/netbsdlike/netbsd/mod.rs b/src/unix/bsd/netbsdlike/netbsd/mod.rs
index 093b24fe95d10..de5ec3863e717 100644
--- a/src/unix/bsd/netbsdlike/netbsd/mod.rs
+++ b/src/unix/bsd/netbsdlike/netbsd/mod.rs
@@ -2422,7 +2422,7 @@ f! {
             .offset(_ALIGN(::mem::size_of::<::cmsghdr>()) as isize)
     }
 
-    pub fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
+    pub {const} fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
         _ALIGN(::mem::size_of::<::cmsghdr>()) as ::c_uint + length
     }
 
diff --git a/src/unix/bsd/netbsdlike/openbsd/mod.rs b/src/unix/bsd/netbsdlike/openbsd/mod.rs
index ef66311268b13..3b87dc211f236 100644
--- a/src/unix/bsd/netbsdlike/openbsd/mod.rs
+++ b/src/unix/bsd/netbsdlike/openbsd/mod.rs
@@ -1705,7 +1705,7 @@ f! {
             .offset(_ALIGN(::mem::size_of::<::cmsghdr>()) as isize)
     }
 
-    pub fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
+    pub {const} fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
         _ALIGN(::mem::size_of::<::cmsghdr>()) as ::c_uint + length
     }
 
diff --git a/src/unix/haiku/mod.rs b/src/unix/haiku/mod.rs
index c1a38f1b360dd..b34b7ca68f3ed 100644
--- a/src/unix/haiku/mod.rs
+++ b/src/unix/haiku/mod.rs
@@ -1504,7 +1504,7 @@ f! {
             as ::c_uint
     }
 
-    pub fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
+    pub {const} fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
         CMSG_ALIGN(::mem::size_of::<cmsghdr>()) as ::c_uint + length
     }
 
diff --git a/src/unix/linux_like/mod.rs b/src/unix/linux_like/mod.rs
index e08bb7dbb05b0..b487da9fa91d9 100644
--- a/src/unix/linux_like/mod.rs
+++ b/src/unix/linux_like/mod.rs
@@ -1557,7 +1557,7 @@ f! {
             as ::c_uint
     }
 
-    pub fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
+    pub {const} fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
         CMSG_ALIGN(::mem::size_of::<cmsghdr>()) as ::c_uint + length
     }
 
diff --git a/src/unix/nto/mod.rs b/src/unix/nto/mod.rs
index b8fcf9df8ee37..5d13568e43943 100644
--- a/src/unix/nto/mod.rs
+++ b/src/unix/nto/mod.rs
@@ -2539,7 +2539,7 @@ f! {
             .offset(_CMSG_ALIGN(::mem::size_of::<::cmsghdr>()) as isize)
     }
 
-    pub fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
+    pub {const} fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
         _CMSG_ALIGN(::mem::size_of::<::cmsghdr>()) as ::c_uint + length
     }
 
diff --git a/src/unix/solarish/mod.rs b/src/unix/solarish/mod.rs
index 48ab4dbb9288c..400de8a26471c 100644
--- a/src/unix/solarish/mod.rs
+++ b/src/unix/solarish/mod.rs
@@ -2601,7 +2601,7 @@ f! {
         _CMSG_DATA_ALIGN(cmsg.offset(1) as usize) as *mut ::c_uchar
     }
 
-    pub fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
+    pub {const} fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
         _CMSG_DATA_ALIGN(::mem::size_of::<::cmsghdr>()) as ::c_uint + length
     }
 
diff --git a/src/vxworks/mod.rs b/src/vxworks/mod.rs
index 6b705e8a22c81..c337a82793e6a 100644
--- a/src/vxworks/mod.rs
+++ b/src/vxworks/mod.rs
@@ -1072,7 +1072,7 @@ f! {
             as ::c_uint
     }
 
-    pub fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
+    pub {const} fn CMSG_LEN(length: ::c_uint) -> ::c_uint {
         CMSG_ALIGN(::mem::size_of::<cmsghdr>()) as ::c_uint + length
     }
 }