diff --git a/activation/files_windows.go b/activation/files_stub.go
similarity index 92%
rename from activation/files_windows.go
rename to activation/files_stub.go
index d391bf00..31db300c 100644
--- a/activation/files_windows.go
+++ b/activation/files_stub.go
@@ -12,6 +12,9 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build windows || plan9
+// +build windows plan9
+
 package activation
 
 import "os"
diff --git a/activation/files_unix.go b/activation/files_unix.go
index bf7671dd..549f1614 100644
--- a/activation/files_unix.go
+++ b/activation/files_unix.go
@@ -12,8 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-//go:build !windows
-// +build !windows
+//go:build !windows && !plan9
+// +build !windows,!plan9
 
 // Package activation implements primitives for systemd socket activation.
 package activation