diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8e7a3c4f74..ace72f332c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased] - ReleaseDate
 ### Added
+- Add `CLK_TCK` to `SysconfVar`
+  (#[1177](https://github.com/nix-rust/nix/pull/1177))
 ### Changed
 ### Fixed
 ### Removed
diff --git a/src/unistd.rs b/src/unistd.rs
index b7fe567b4d..2dd5064b76 100644
--- a/src/unistd.rs
+++ b/src/unistd.rs
@@ -1994,7 +1994,8 @@ pub enum SysconfVar {
     BC_STRING_MAX = libc::_SC_BC_STRING_MAX,
     /// Maximum number of simultaneous processes per real user ID.
     CHILD_MAX = libc::_SC_CHILD_MAX,
-    // _SC_CLK_TCK is obsolete
+    // The number of clock ticks per second.
+    CLK_TCK = libc::_SC_CLK_TCK,
     /// Maximum number of weights that can be assigned to an entry of the
     /// LC_COLLATE order keyword in the locale definition file
     COLL_WEIGHTS_MAX = libc::_SC_COLL_WEIGHTS_MAX,