diff --git a/metric/common.go b/metric/common.go
index d708c4d..5cceb59 100644
--- a/metric/common.go
+++ b/metric/common.go
@@ -33,7 +33,10 @@ type MetricPipe struct {
 }
 
 func (mp MetricPipe) Close() {
-	mp.pipe.Close()
+	if mp.pipe != nil {
+		mp.pipe.Close()
+		mp.pipe = nil
+	}
 }
 
 func (mp MetricPipe) writeLine(line string) {