diff --git a/hugr/build.rs b/hugr/build.rs
new file mode 100644
index 000000000..385ec3d50
--- /dev/null
+++ b/hugr/build.rs
@@ -0,0 +1,7 @@
+//! Build script for the `hugr` crate.
+
+fn main() {
+    // We use a `ci_run` RUSTFLAG to indicate that we are running a CI check,
+    // so we can reject debug code using some tools defined in `utils.rs`.
+    println!("cargo:rustc-check-cfg=cfg(ci_run)");
+}