diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e66283f..4ba6173 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -1,17 +1,28 @@
 name: CI
 
-on: [push, pull_request]
+on:
+  push:
+    branches:
+    - 'master'
+  pull_request:
+    branches:
+    - 'master'
+
+env:
+  # GHA enables the sparse registry by default; make sure that also works for older nightlies.
+  CARGO_UNSTABLE_SPARSE_REGISTRY: 'true'
 
 jobs:
   test:
     name: Test Suite
     strategy:
+      fail-fast: false
       matrix:
         rust:
           - nightly
+          - nightly-2023-01-01
           - nightly-2022-07-01
           - nightly-2022-01-01
-          - nightly-2021-07-01
         os:
           - ubuntu-latest
           - macos-latest
diff --git a/src/lib.rs b/src/lib.rs
index 75dc8a6..9d6b0dc 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -248,6 +248,7 @@ impl SysrootBuilder {
         )
         .context("failed to copy lockfile from sysroot source")?;
         make_writeable(&lock_file).context("failed to make lockfile writeable")?;
+        let have_sysroot_crate = src_dir.join("sysroot").exists();
         let crates = match &self.config {
             SysrootConfig::NoStd => format!(
                 r#"
@@ -262,6 +263,19 @@ version = "*"
                 src_dir_core = src_dir.join("core"),
                 src_dir_alloc = src_dir.join("alloc"),
             ),
+            SysrootConfig::WithStd { std_features } if have_sysroot_crate => format!(
+                r#"
+[dependencies.std]
+features = {std_features:?}
+path = {src_dir_std:?}
+[dependencies.sysroot]
+path = {src_dir_sysroot:?}
+                "#,
+                std_features = std_features,
+                src_dir_std = src_dir.join("std"),
+                src_dir_sysroot = src_dir.join("sysroot"),
+            ),
+            // Fallback for old rustc where the main crate was `test`, not `sysroot`
             SysrootConfig::WithStd { std_features } => format!(
                 r#"
 [dependencies.std]
@@ -279,7 +293,7 @@ path = {src_dir_test:?}
             r#"
 [package]
 authors = ["rustc-build-sysroot"]
-name = "sysroot"
+name = "custom-local-sysroot"
 version = "0.0.0"
 
 [lib]