diff --git a/.external-types.toml b/.external-types.toml
deleted file mode 100644
index 679f43e..0000000
--- a/.external-types.toml
+++ /dev/null
@@ -1,9 +0,0 @@
-# cargo-check-external-types configuration
-# https://crates.io/crates/cargo-check-external-types
-
-# The following are external types that are allowed to be exposed in our public API.
-allowed_external_types = [
-    "proc_macro2::*",
-    "quote::*",
-    "syn::*",
-]
diff --git a/Cargo.toml b/Cargo.toml
index 0c7caa0..69d26bd 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -16,6 +16,14 @@ Providing the features between \"full\" and \"derive\" of syn.
 all-features = true
 targets = ["x86_64-unknown-linux-gnu"]
 
+[package.metadata.cargo_check_external_types]
+# The following are external types that are allowed to be exposed in our public API.
+allowed_external_types = [
+    "proc_macro2::*",
+    "quote::*",
+    "syn::*",
+]
+
 [workspace]
 resolver = "2"
 members = ["examples/const_fn"]