diff --git a/proto/pointer_reflect.go b/proto/pointer_reflect.go
index 749919d..9899141 100644
--- a/proto/pointer_reflect.go
+++ b/proto/pointer_reflect.go
@@ -29,7 +29,7 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-// +build appengine
+// +build appengine js
 
 // This file contains an implementation of proto field accesses using package reflect.
 // It is slower than the code in pointer_unsafe.go but it avoids package unsafe and can
diff --git a/proto/pointer_unsafe.go b/proto/pointer_unsafe.go
index e9be0fe..ceece77 100644
--- a/proto/pointer_unsafe.go
+++ b/proto/pointer_unsafe.go
@@ -29,7 +29,7 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-// +build !appengine
+// +build !appengine,!js
 
 // This file contains the implementation of the proto field accesses using package unsafe.