diff --git a/tools/tht/internal/safeio/private_root_windows.go b/tools/tht/internal/safeio/private_root_windows.go
index abde8098..1d6d9af2 100644
--- a/tools/tht/internal/safeio/private_root_windows.go
+++ b/tools/tht/internal/safeio/private_root_windows.go
@@ -203,7 +203,11 @@ func openWindowsRelativeObjectWithShareMode(
 		attributes,
 		&status,
 		&allocationSize,
-		windows.FILE_ATTRIBUTE_NORMAL,
+		// NtCreateFile expects zero here for the retained open/create contract. The
+		// Win32 FILE_ATTRIBUTE_NORMAL flag is not a valid NT FileAttributes value
+		// for this RootDirectory-relative call and produces STATUS_INVALID_PARAMETER
+		// on the Windows runner.
+		0,
 		shareMode,
 		disposition,
 		options,