diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 91c086f5..195b12c5 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -63,7 +63,7 @@ jobs:
       - name: Install rust toolchain
         uses: dtolnay/rust-toolchain@master
         with:
-          toolchain: nightly-2024-05-01
+          toolchain: nightly-2024-06-30
           # ^ sync with https://github.com/awslabs/cargo-check-external-types/blob/main/rust-toolchain.toml
       - run: cargo install --locked cargo-check-external-types
       - name: run cargo-check-external-types for rcgen/