diff --git a/pb_appengine.go b/pb_appengine.go
index 17168f3..e8dd9ea 100644
--- a/pb_appengine.go
+++ b/pb_appengine.go
@@ -1,11 +1,12 @@
-// +build appengine js
+// +build appengine js wasip1
 
 package pb
 
 import "errors"
 
 // terminalWidth returns width of the terminal, which is not supported
-// and should always failed on appengine classic which is a sandboxed PaaS.
+// and should always failed on appengine classic which is a sandboxed PaaS,
+// and on wasip1 which has no terminal-size API.
 func terminalWidth() (int, error) {
 	return 0, errors.New("Not supported")
 }