diff --git a/plan9/syscall_plan9.go b/plan9/syscall_plan9.go
index d39d07de..84e14714 100644
--- a/plan9/syscall_plan9.go
+++ b/plan9/syscall_plan9.go
@@ -12,6 +12,7 @@
 package plan9
 
 import (
+	"bytes"
 	"syscall"
 	"unsafe"
 )
@@ -50,12 +51,11 @@ func atoi(b []byte) (n uint) {
 }
 
 func cstring(s []byte) string {
-	for i := range s {
-		if s[i] == 0 {
-			return string(s[0:i])
-		}
+	i := bytes.IndexByte(s, 0)
+	if i == -1 {
+		i = len(s)
 	}
-	return string(s)
+	return string(s[:i])
 }
 
 func errstr() string {