diff --git a/Results/Entities/MeterTestRslt.cs b/Results/Entities/MeterTestRslt.cs
index 26c687b89..e3f84d0c1 100644
--- a/Results/Entities/MeterTestRslt.cs
+++ b/Results/Entities/MeterTestRslt.cs
@@ -170,7 +170,7 @@ namespace Results.Entities
             writer.Write(LastError);
 #endif
             writer.Write((TestRslt != null && TestRslt.Name() != null) ? TestRslt.Name() : string.Empty);
-            writer.Write(TestRslt.Part);
+            writer.Write(TestRslt != null ? TestRslt.Part : 0);
         }
 
         public virtual void ReadBinary(BinaryReader reader, IList<TestRslt> testResults)