diff --git a/CHANGELOG.md b/CHANGELOG.md
index 44daf09..74ec985 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   (#18).
 
 ### Changed
+- `mach.toml` declares the compiler range `mach = "^5.3"`, so mach 5.3 and
+  later no longer warn on every build (#20).
 - Releases run through the family's shared release workflow. A pushed `v*`
   tag checks the tag against the manifest version and the CHANGELOG, runs
   every CI leg, and publishes the GitHub release with the CHANGELOG section
diff --git a/mach.toml b/mach.toml
index 944f41f..4293c61 100644
--- a/mach.toml
+++ b/mach.toml
@@ -1,6 +1,7 @@
 [project]
 id = "bench"
 version = "0.1.1"
+mach = "^5.3"
 src = "src"
 out = "out/{target.name}/{profile.name}"