diff --git a/.github/workflows/ci-toolchain.yml b/.github/workflows/ci-toolchain.yml
index 803111b91..c3b3fa659 100644
--- a/.github/workflows/ci-toolchain.yml
+++ b/.github/workflows/ci-toolchain.yml
@@ -43,6 +43,7 @@ jobs:
       uses: alire-project/alr-install@v1
       with:
         crates: gnat_native^${{matrix.gcc_version}} gprbuild
+        cache: false
 
     - name: Build alr with toolchain from `alr install`
       shell: bash
diff --git a/.github/workflows/nightly.yml b/.github/workflows/nightly.yml
index d44685008..b9d9e1dfd 100644
--- a/.github/workflows/nightly.yml
+++ b/.github/workflows/nightly.yml
@@ -21,14 +21,14 @@ jobs:
       fail-fast: false # Attempt to generate as many of them as possible
       matrix:
         os:
-          - macos-14
           - macos-12
+          - macos-14
           - ubuntu-20.04
           - windows-latest
 
     steps:
     - name: Check out repository
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
       with:
         submodules: true
 
@@ -36,19 +36,23 @@ jobs:
       uses: alire-project/alr-install@v1
       with:
         crates: gnat_native gprbuild
+        prefix: alire_prefix
 
-    - name: Replace toolchain with aarch64
-      if: ${{ runner.arch == 'ARM64' }}
+    - name: Display toolchain configuration and verify matching arch
+      shell: bash
       run: |
-          curl -L https://github.com/alire-project/GNAT-FSF-builds/releases/download/gnat-14.1.0-3/gnat-aarch64-darwin-14.1.0-3.tar.gz \
-           | tar xzf - --strip-components=1 -C /Users/runner/work/alire/alire/alire_prefix
-          curl -L https://github.com/alire-project/GNAT-FSF-builds/releases/download/gprbuild-24.0.0-1/gprbuild-aarch64-darwin-24.0.0-1.tar.gz \
-           | tar xzf - --strip-components=1 -C /Users/runner/work/alire/alire/alire_prefix
-          which gcc
-          gcc -v
+        case ${{runner.arch}} in
+          X64)   target_arch=x86_64;;
+          ARM64) target_arch=aarch64;;
+          *)     echo "Unknown arch" && exit 1;;
+        esac
+        which gcc
+        gcc -v
+        gcc -dumpmachine   && gcc -dumpmachine   | grep -q $target_arch || exit 1
+        gprbuild --version && gprbuild --version | grep -q $target_arch || exit 1
 
     - name: Install Python 3.x (required for the testsuite)
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@v5
       with:
         python-version: '3.x'
 
@@ -56,6 +60,13 @@ jobs:
       run: scripts/ci-github.sh
       shell: bash
 
+    # Ascertain whether alr can run without the toolchain that built it
+    - name: Remove toolchain used for building & testing
+      shell: bash
+      run: |
+        rm -rf alire_prefix
+        which gnat || { echo "Toolchain purged"; ./bin/alr version; }
+
     - name: Upload logs (if failed)
       if: failure()
       uses: actions/upload-artifact@v4