diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 536c082..f966166 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -38,7 +38,16 @@ jobs:
           for m in modasm moddet moddis moddsk modren modtok modsfr modsct modscr modscrh; do
             test -s "build/${m}.prg"
           done
-          echo "All PRGs and the disk image are present."
+          # The default build also carries the C128 set and its boot sector
+          # on the same disk, so a C128-only breakage must fail the release
+          # too (same checks as build.yml).
+          test -s build/c128/editor.prg
+          for m in modasm moddet moddis moddsk modren modtok modsfr; do
+            test -s "build/c128/${m}.prg"
+          done
+          test -s build/c128/boot128.bin
+          head -c 3 build/c128/boot128.bin | grep -q CBM
+          echo "All PRGs (C64 + C128), the boot sector and the disk image are present."
 
       - name: Stamp versioned disk image
         run: cp petproject.d64 "petproject-${GITHUB_REF_NAME}.d64"