diff --git a/metrics/influx/influx.go b/metrics/influx/influx.go
index 0c555e116..b9a3f6698 100644
--- a/metrics/influx/influx.go
+++ b/metrics/influx/influx.go
@@ -168,10 +168,14 @@ func mergeTags(tags map[string]string, labelValues []string) map[string]string {
 	if len(labelValues)%2 != 0 {
 		panic("mergeTags received a labelValues with an odd number of strings")
 	}
+	ret := make(map[string]string, len(tags)+len(labelValues)/2)
+	for k, v := range tags {
+		ret[k] = v
+	}
 	for i := 0; i < len(labelValues); i += 2 {
-		tags[labelValues[i]] = labelValues[i+1]
+		ret[labelValues[i]] = labelValues[i+1]
 	}
-	return tags
+	return ret
 }
 
 func sum(a []float64) float64 {
diff --git a/metrics/influx/influx_test.go b/metrics/influx/influx_test.go
index b5d3df4e2..57950f30c 100644
--- a/metrics/influx/influx_test.go
+++ b/metrics/influx/influx_test.go
@@ -82,6 +82,37 @@ func TestHistogramLabels(t *testing.T) {
 	}
 }
 
+func TestIssue404(t *testing.T) {
+	in := New(map[string]string{}, influxdb.BatchPointsConfig{}, log.NewNopLogger())
+
+	counterOne := in.NewCounter("influx_counter_one").With("a", "b")
+	counterOne.Add(123)
+
+	counterTwo := in.NewCounter("influx_counter_two").With("c", "d")
+	counterTwo.Add(456)
+
+	w := &bufWriter{}
+	in.WriteTo(w)
+
+	lines := strings.Split(strings.TrimSpace(w.buf.String()), "\n")
+	if want, have := 2, len(lines); want != have {
+		t.Fatalf("want %d, have %d", want, have)
+	}
+	for _, line := range lines {
+		if strings.HasPrefix(line, "influx_counter_one") {
+			if !strings.HasPrefix(line, "influx_counter_one,a=b count=123 ") {
+				t.Errorf("invalid influx_counter_one: %s", line)
+			}
+		} else if strings.HasPrefix(line, "influx_counter_two") {
+			if !strings.HasPrefix(line, "influx_counter_two,c=d count=456 ") {
+				t.Errorf("invalid influx_counter_two: %s", line)
+			}
+		} else {
+			t.Errorf("unexpected line: %s", line)
+		}
+	}
+}
+
 type bufWriter struct {
 	buf bytes.Buffer
 }