diff --git a/Cargo.toml b/Cargo.toml
index 4dfe5654a..d3cf7c95b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -14,8 +14,9 @@ license = "Apache-2.0"
 # authors
 
 [workspace.lints.rust]
-missing_docs = "warn"
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(ci_run)'] }
 
+missing_docs = "warn"
 [workspace.lints.clippy]
 # Unstable check, may cause false positives.
 # https://github.com/rust-lang/rust-clippy/issues/5112
diff --git a/hugr-core/build.rs b/hugr-core/build.rs
deleted file mode 100644
index 385ec3d50..000000000
--- a/hugr-core/build.rs
+++ /dev/null
@@ -1,7 +0,0 @@
-//! 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)");
-}