diff --git a/src/syscall/env_plan9.go b/src/syscall/env_plan9.go
index 3044b410a9..9345079052 100644
--- a/src/syscall/env_plan9.go
+++ b/src/syscall/env_plan9.go
@@ -128,6 +128,7 @@ func Setenv(key, value string) error {
 	}
 	env[key] = value
 	envs = append(envs, key+"="+value)
+	envi[key] = len(envs) - 1
 	return nil
 }