diff --git a/.github/workflows/build-windows.yml b/.github/workflows/build-windows.yml
index 2f47d0a3..0d67fca4 100644
--- a/.github/workflows/build-windows.yml
+++ b/.github/workflows/build-windows.yml
@@ -22,10 +22,13 @@ concurrency:
 
 defaults:
   run:
-    # Git Bash is installed alongside Git on the runner. Using bash keeps
-    # the steps parallel to build-android.yml / build-ios-sim.yml. PowerShell
-    # is available per-step via `shell: powershell` if needed.
-    shell: bash
+    # Explicit Git Bash path (not `shell: bash`) because Windows resolves
+    # bare `bash` to C:\Windows\System32\bash.exe (WSL), which refuses to
+    # run when the act_runner service is hosted under LocalSystem:
+    #   "Running WSL as local system is not supported."
+    # Git Bash works fine under LocalSystem and matches how GitHub's
+    # hosted windows-latest runner invokes bash.
+    shell: '"C:\Program Files\Git\bin\bash.exe" --noprofile --norc -eo pipefail {0}'
 
 jobs:
   build: