diff --git a/.forgejo/workflows/auto-update.yaml b/.forgejo/workflows/auto-update.yaml
index 7b9733d..aeb30dd 100644
--- a/.forgejo/workflows/auto-update.yaml
+++ b/.forgejo/workflows/auto-update.yaml
@@ -11,7 +11,7 @@ jobs:
     runs-on: nix
     outputs:
       changed: ${{ steps.changes.outputs.changed }}
-      hosts: ${{ steps.hosts.outputs.hosts }}
+      hosts: ${{ steps.hosts.outputs.hosts || '[]' }}
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
@@ -39,9 +39,22 @@ jobs:
         id: hosts
         if: steps.changes.outputs.changed == 'true'
         run: |
-          HOSTS=$(nix eval --json .#colmena --apply 'x: builtins.filter (n: n != "meta" && builtins.elem "lxc" (x.${n}.deployment.tags or [])) (builtins.attrNames x)')
+          set -euo pipefail
+          HOSTS=$(nix eval --json .#colmena --apply 'x: builtins.filter (n: n != "meta" && builtins.elem "lxc" (x.${n}.deployment.tags or [])) (builtins.attrNames x)' 2>&1) || {
+            echo "Failed to evaluate colmena hosts"
+            exit 1
+          }
+          # Validate the output is a non-empty JSON array
+          if ! echo "$HOSTS" | jq -e '. | if type == "array" and length > 0 then true else false end' > /dev/null 2>&1; then
+            echo "Error: No LXC hosts found or invalid JSON output: $HOSTS"
+            echo "hosts=[]" >> $GITHUB_OUTPUT
+            exit 0
+          fi
           echo "hosts=$HOSTS" >> $GITHUB_OUTPUT
           echo "Discovered hosts: $HOSTS"
+          # Verify output was set
+          echo "DEBUG: GITHUB_OUTPUT contents:"
+          cat $GITHUB_OUTPUT
 
       - name: Upload flake.lock
         if: steps.changes.outputs.changed == 'true'
@@ -53,13 +66,21 @@ jobs:
 
   build:
     needs: check-updates
-    if: needs.check-updates.outputs.changed == 'true'
+    if: needs.check-updates.outputs.changed == 'true' && needs.check-updates.outputs.hosts != '[]' && needs.check-updates.outputs.hosts != ''
     runs-on: nix
     strategy:
       fail-fast: false
       matrix:
-        host: ${{ fromJson(needs.check-updates.outputs.hosts) }}
+        host: ${{ fromJson(needs.check-updates.outputs.hosts || '[]') }}
     steps:
+      - name: Debug - show received values
+        run: |
+          echo "=== DEBUG: Values received from check-updates job ==="
+          echo "needs.check-updates.outputs.changed = '${{ needs.check-updates.outputs.changed }}'"
+          echo "needs.check-updates.outputs.hosts = '${{ needs.check-updates.outputs.hosts }}'"
+          echo "matrix.host = '${{ matrix.host }}'"
+          echo "=== END DEBUG ==="
+
       - name: Checkout repository
         uses: actions/checkout@v4
 
@@ -71,8 +92,16 @@ jobs:
       - name: Build ${{ matrix.host }}
         id: build
         run: |
-          echo "Building host: ${{ matrix.host }}"
-          nix build .#nixosConfigurations.${{ matrix.host }}.config.system.build.toplevel --no-link 2>&1 | tee build-output.txt
+          HOST="${{ matrix.host }}"
+          echo "DEBUG: matrix.host='$HOST'"
+          echo "DEBUG: raw matrix.host='${{ matrix.host }}'"
+          if [ -z "$HOST" ]; then
+            echo "Error: Host name is empty"
+            echo "This usually means the 'hosts' output from check-updates job was not received properly"
+            exit 1
+          fi
+          echo "Building host: $HOST"
+          nix build ".#nixosConfigurations.${HOST}.config.system.build.toplevel" --no-link 2>&1 | tee build-output.txt
         continue-on-error: true
 
       - name: Upload build log on failure