diff --git a/spew/bypass.go b/spew/bypass.go
index 565bf58..1de6e02 100644
--- a/spew/bypass.go
+++ b/spew/bypass.go
@@ -13,9 +13,9 @@
 // OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 
 // NOTE: Due to the following build constraints, this file will only be compiled
-// when the code is not running on Google App Engine and "-tags disableunsafe"
-// is not added to the go build command line.
-// +build !appengine,!disableunsafe
+// when the code is not running on Google App Engine, compiled by GopherJS, and
+// "-tags disableunsafe" is not added to the go build command line.
+// +build !appengine,!disableunsafe,!js
 
 package spew
 
diff --git a/spew/bypasssafe.go b/spew/bypasssafe.go
index 457e412..adef4c4 100644
--- a/spew/bypasssafe.go
+++ b/spew/bypasssafe.go
@@ -13,9 +13,9 @@
 // OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 
 // NOTE: Due to the following build constraints, this file will only be compiled
-// when either the code is running on Google App Engine or "-tags disableunsafe"
-// is added to the go build command line.
-// +build appengine disableunsafe
+// when the code is running on Google App Engine, compiled by GopherJS, or
+// "-tags disableunsafe" is added to the go build command line.
+// +build appengine disableunsafe js
 
 package spew
 
diff --git a/spew/internalunsafe_test.go b/spew/internalunsafe_test.go
index 83e070e..ddaa41d 100644
--- a/spew/internalunsafe_test.go
+++ b/spew/internalunsafe_test.go
@@ -13,9 +13,9 @@
 // OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 
 // NOTE: Due to the following build constraints, this file will only be compiled
-// when the code is not running on Google App Engine and "-tags disableunsafe"
-// is not added to the go build command line.
-// +build !appengine,!disableunsafe
+// when the code is not running on Google App Engine, compiled by GopherJS, and
+// "-tags disableunsafe" is not added to the go build command line.
+// +build !appengine,!disableunsafe,!js
 
 /*
 This test file is part of the spew package rather than than the spew_test