diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index cfe06b1..521e3f6 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -1,7 +1,7 @@
 name: CI
 
 on:
-  push:
+  push: { branches: [main] }
   pull_request:
   schedule: [cron: "40 1 * * *"]
 
@@ -12,54 +12,61 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust: [
+        rust:
           # Test with toolchain file override
-          "",
+          - null
+
           # Test that the sparse registry check works.
           # 1.66 and 1.67 don't support stable sparse registry.
-          "1.66",
-          "nightly",
-          "beta",
-          "stable",
-        ]
-        os: [
-          "ubuntu-latest",
-          "windows-latest",
-          "macos-latest",
-        ]
+          - "1.66"
+
+          - "nightly"
+          - "beta"
+          - "stable"
+        os:
+          - ubuntu-latest
+          - windows-latest
+          - macos-latest
     steps:
       - uses: actions/checkout@v4
+
       # Test toolchain file support
       - name: Write rust-toolchain.toml
+        if: matrix.rust == null
+        shell: bash
         run: |
           cat <<EOF >>rust-toolchain.toml
           [toolchain]
-          channel = "nightly-2022-09-10"
+          channel = "nightly-2024-01-11"
           components = [ "rustfmt", "rustc-dev" ]
           targets = [ "wasm32-unknown-unknown", "thumbv7m-none-eabi" ]
           profile = "minimal"
           EOF
-        shell: bash
-        if: matrix.rust == ''
 
-      - uses: ./
+      - id: toolchain
         name: Run actions-rust-lang/setup-rust-toolchain ${{matrix.rust || 'on toolchain file'}}
-        id: toolchain
+        uses: ./
         with:
           toolchain: ${{matrix.rust}}
           components: clippy
+
       - name: Check ${{'${{steps.toolchain.outputs.rustc-version}}'}}
         run: echo '${{steps.toolchain.outputs.rustc-version}}'
+
       - name: Check ${{'${{steps.toolchain.outputs.cargo-version}}'}}
         run: echo '${{steps.toolchain.outputs.cargo-version}}'
+
       - name: Check ${{'${{steps.toolchain.outputs.rustup-version}}'}}
         run: echo '${{steps.toolchain.outputs.rustup-version}}'
-      - run: rustc --version && cargo --version
-        shell: bash
+
+      - shell: bash
+        run: rustc --version && cargo --version
 
       # Test with creating a small project
       - run: cargo init . --bin --name ci
+
       # Add tiny empty crate.
       # This checks that registry access works.
       - run: cargo add serde_as
+
       - run: cargo clippy
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5e580c5..7a49699 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+* Allow overriding the toolchain file with explicit `toolchain` input. (#26)
+
 ## [1.6.0] - 2023-12-04
 
 ### Added
diff --git a/action.yml b/action.yml
index 2331188..45eda54 100644
--- a/action.yml
+++ b/action.yml
@@ -59,17 +59,21 @@ runs:
       shell: bash
 
     - id: flags
+      env:
+        targets: ${{inputs.target}}
+        components: ${{inputs.components}}
+      shell: bash
       run: |
         : construct rustup command line
         echo "targets=$(for t in ${targets//,/ }; do echo -n ' --target' $t; done)" >> $GITHUB_OUTPUT
         echo "components=$(for c in ${components//,/ }; do echo -n ' --component' $c; done)" >> $GITHUB_OUTPUT
         echo "downgrade=${{inputs.toolchain == 'nightly' && inputs.components && ' --allow-downgrade' || ''}}" >> $GITHUB_OUTPUT
-      env:
-        targets: ${{inputs.target}}
-        components: ${{inputs.components}}
-      shell: bash
+
     # The environment variables always need to be set before the caching action
-    - name: "Setting Environment Variables"
+    - name: Setting Environment Variables
+      env:
+        NEW_RUSTFLAGS: ${{inputs.rustflags}}
+      shell: bash
       run: |
         if [[ ! -v CARGO_INCREMENTAL ]]; then
           echo "CARGO_INCREMENTAL=0" >> $GITHUB_ENV
@@ -95,23 +99,27 @@ runs:
         if [[ ! -v CARGO_REGISTRIES_CRATES_IO_PROTOCOL ]]; then
           echo "CARGO_REGISTRIES_CRATES_IO_PROTOCOL=sparse" >> $GITHUB_ENV
         fi
-      shell: bash
-      env:
-        NEW_RUSTFLAGS: ${{inputs.rustflags}}
-    - name: "Install Rust Problem Matcher"
+
+    - name: Install Rust Problem Matcher
       if: inputs.matcher == 'true'
-      run: echo "::add-matcher::${{ github.action_path }}/rust.json"
       shell: bash
+      run: echo "::add-matcher::${{ github.action_path }}/rust.json"
 
     - name: Install rustup, if needed
+      if: runner.os != 'Windows'
+      shell: bash
       run: |
         if ! command -v rustup &> /dev/null ; then
           curl --proto '=https' --tlsv1.2 --retry 10 --retry-connrefused -fsSL "https://sh.rustup.rs" | sh -s -- --default-toolchain none -y
           echo "${CARGO_HOME:-$HOME/.cargo}/bin" >> $GITHUB_PATH
         fi
-      if: runner.os != 'Windows'
-      shell: bash
+
     - name: rustup toolchain install ${{inputs.toolchain || 'stable'}}
+      env:
+        toolchain: ${{inputs.toolchain}}
+        targets: ${{inputs.target}}
+        components: ${{inputs.components}}
+      shell: bash
       run: |
         if [[ -z "$toolchain" && ( -f "rust-toolchain" || -f "rust-toolchain.toml" ) ]]
         then
@@ -132,14 +140,10 @@ runs:
           rustup toolchain install $toolchain${{steps.flags.outputs.targets}}${{steps.flags.outputs.components}} --profile minimal${{steps.flags.outputs.downgrade}} --no-self-update
           rustup default $toolchain
         fi
-      env:
-        toolchain: ${{inputs.toolchain}}
-        targets: ${{inputs.target}}
-        components: ${{inputs.components}}
-      shell: bash
 
-    - name: Print installed versions
-      id: versions
+    - id: versions
+      name: Print installed versions
+      shell: bash
       run: |
         echo "rustc-version=$(rustc --version)" >> $GITHUB_OUTPUT
         rustc --version --verbose
@@ -151,9 +155,9 @@ runs:
         DATE=$(rustc --version --verbose | sed -ne 's/^commit-date: \(20[0-9][0-9]\)-\([01][0-9]\)-\([0-3][0-9]\)$/\1\2\3/p')
         HASH=$(rustc --version --verbose | sed -ne 's/^commit-hash: //p')
         echo "cachekey=$(echo $DATE$HASH | head -c12)" >> $GITHUB_OUTPUT
-      shell: bash
 
-    - name: "Downgrade registry access protocol when needed"
+    - name: Downgrade registry access protocol when needed
+      shell: bash
       run: |
         # Not all versions support setting CARGO_REGISTRIES_CRATES_IO_PROTOCOL
         # On versions 1.66, 1.67, and 1.68.0-nightly the value "sparse" is still unstable.
@@ -163,8 +167,7 @@ runs:
           echo "Downgrade cargo registry protocol to git"
           echo "CARGO_REGISTRIES_CRATES_IO_PROTOCOL=git" >> $GITHUB_ENV
         fi
-      shell: bash
 
-    - name: "Setup Rust Caching"
+    - name: Setup Rust Caching
       if: inputs.cache == 'true'
       uses: Swatinem/rust-cache@v2