diff --git a/net/net_test.go b/net/net_test.go
index bf466504..fbecd1e6 100644
--- a/net/net_test.go
+++ b/net/net_test.go
@@ -89,8 +89,12 @@ func TestNetIOCountersAll(t *testing.T) {
 	}
 	// small diff is ok
 	if math.Abs(float64(v[0].PacketsRecv-pr)) > 5 {
-		// This test often fails in CI. so just print even if failed
-		fmt.Printf("invalid sum value: %v, %v", v[0].PacketsRecv, pr)
+		if ci := os.Getenv("CI"); ci != "" {
+			// This test often fails in CI. so just print even if failed.
+			fmt.Printf("invalid sum value: %v, %v", v[0].PacketsRecv, pr)
+		} else {
+			t.Errorf("invalid sum value: %v, %v", v[0].PacketsRecv, pr)
+		}
 	}
 }
 
diff --git a/v3/net/net_test.go b/v3/net/net_test.go
index abcfc82f..fff0c88b 100644
--- a/v3/net/net_test.go
+++ b/v3/net/net_test.go
@@ -89,8 +89,12 @@ func TestNetIOCountersAll(t *testing.T) {
 	}
 	// small diff is ok
 	if math.Abs(float64(v[0].PacketsRecv-pr)) > 5 {
-		// This test often fails in CI. so just print even if failed
-		fmt.Printf("invalid sum value: %v, %v", v[0].PacketsRecv, pr)
+		if ci := os.Getenv("CI"); ci != "" {
+			// This test often fails in CI. so just print even if failed.
+			fmt.Printf("invalid sum value: %v, %v", v[0].PacketsRecv, pr)
+		} else {
+			t.Errorf("invalid sum value: %v, %v", v[0].PacketsRecv, pr)
+		}
 	}
 }