diff --git a/.gitea/workflows/build.yml b/.gitea/workflows/build.yml
index f5d34b989..25c17a424 100644
--- a/.gitea/workflows/build.yml
+++ b/.gitea/workflows/build.yml
@@ -71,11 +71,19 @@ jobs:
       - name: Install vcpkg native deps
         shell: powershell
         run: |
-          # --feature-flags=-manifests forces classic mode -- the repo
-          # has a vcpkg.json that pulls in ffmpeg+amf+nvcodec+qsv (hwcodec
-          # path) which is a 2hr build and not needed for Sciter UI.
-          # Sciter only needs the codec/image libs below.
-          C:\vcpkg\vcpkg.exe install --feature-flags=-manifests --triplet x64-windows-static libvpx libyuv opus aom libjpeg-turbo
+          # Force classic mode -- the repo has a vcpkg.json that pulls
+          # in ffmpeg+amf+nvcodec+qsv (hwcodec) which is a 2hr build and
+          # not needed for Sciter UI. The CLI flag --feature-flags is
+          # ignored by some vcpkg versions when manifest is auto-detected;
+          # env var VCPKG_FEATURE_FLAGS=-manifests is honored reliably.
+          # Also run from C:\ so vcpkg's upward-walk can't find the
+          # repo's vcpkg.json.
+          $env:VCPKG_FEATURE_FLAGS = "-manifests"
+          Push-Location C:\
+          try {
+            C:\vcpkg\vcpkg.exe install --triplet x64-windows-static libvpx libyuv opus aom libjpeg-turbo
+            if ($LASTEXITCODE -ne 0) { throw "vcpkg install failed (exit $LASTEXITCODE)" }
+          } finally { Pop-Location }
 
       - name: cargo build --release (Sciter UI)
         shell: powershell