diff --git a/internal/devicescale/impl_plan9.go b/internal/devicescale/impl_plan9.go
new file mode 100644
index 000000000..72e1f4a3e
--- /dev/null
+++ b/internal/devicescale/impl_plan9.go
@@ -0,0 +1,21 @@
+// Copyright 2018 The Ebiten Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build !js
+
+package devicescale
+
+func impl(x, y int) float64 {
+	return 1
+}