diff --git a/cpu/cpu_wasm.go b/cpu/cpu_wasm.go
index 108d9e69..bd9bbda0 100644
--- a/cpu/cpu_wasm.go
+++ b/cpu/cpu_wasm.go
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build wasm
+
 package cpu
 
 // We're compiling the cpu package for an unknown (software-abstracted) CPU.