diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index a7ff1fb..60eb41e 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -62,6 +62,10 @@ jobs:
         run: |
           $tag = if ($env:GITHUB_REF_NAME -and $env:GITHUB_REF_NAME -ne '') { $env:GITHUB_REF_NAME } else { 'dev' }
           $num = $tag -replace '^v', ''
+          # `num` feeds Inno's VersionInfoVersion, which must be numeric X.Y[.Z[.W]].
+          # Branch / workflow_dispatch refs (e.g. "master") aren't versions, so fall
+          # back to 0.0.0 for those; real vX.Y.Z tags pass through unchanged.
+          if ($num -notmatch '^[0-9]+(\.[0-9]+){1,3}$') { $num = '0.0.0' }
           "tag=$tag" | Out-File -FilePath $env:GITHUB_OUTPUT -Append
           "num=$num" | Out-File -FilePath $env:GITHUB_OUTPUT -Append