diff --git a/src/cmd/go/testdata/script/env_write.txt b/src/cmd/go/testdata/script/env_write.txt
index 2e8b439113..5d40949cdd 100644
--- a/src/cmd/go/testdata/script/env_write.txt
+++ b/src/cmd/go/testdata/script/env_write.txt
@@ -173,6 +173,7 @@ go env -w GOOS=linux GOARCH=mips
 env GOOS=windows
 ! go env -u GOOS
 stderr 'unsupported GOOS/GOARCH.*windows/mips$'
+env GOOS=
 
 # go env -w should reject relative paths in GOMODCACHE environment.
 ! go env -w GOMODCACHE=~/test