diff --git a/cuprate/build.rs b/cuprate/build.rs
new file mode 100644
index 0000000..f0e8751
--- /dev/null
+++ b/cuprate/build.rs
@@ -0,0 +1,15 @@
+// This sets the git `COMMIT` environment variable.
+fn main() {
+	println!("cargo:rerun-if-changed=../.git/refs/heads/");
+
+	let output = std::process::Command::new("git")
+		.arg("rev-parse")
+		.arg("HEAD")
+		.output()
+		.unwrap();
+
+	let commit = String::from_utf8(output.stdout).unwrap();
+	assert!(commit.len() >= 40);
+
+	println!("cargo:rustc-env=COMMIT={commit}");
+}