diff --git a/src/EPR.Calculator.API/Exporter/CalcResultsExporter.cs b/src/EPR.Calculator.API/Exporter/CalcResultsExporter.cs
index ba9a103..4f7e763 100644
--- a/src/EPR.Calculator.API/Exporter/CalcResultsExporter.cs
+++ b/src/EPR.Calculator.API/Exporter/CalcResultsExporter.cs
@@ -65,7 +65,7 @@ private static void AppendCsvLine(StringBuilder csvContent, string label, string
         }
         private static string GetResultFileName(int runId)
         {
-            return $"{runId}-{DateTime.Now:yyyy-MM-dd-HHmm}";
+            return $"{runId}-{DateTime.Now:yyyy-MM-dd-HHmm}.csv";
         }
     }
 }