diff --git a/src/js/Misc/MapiTypeConverter.ts b/src/js/Misc/MapiTypeConverter.ts
index 795972ef..3b6fa521 100644
--- a/src/js/Misc/MapiTypeConverter.ts
+++ b/src/js/Misc/MapiTypeConverter.ts
@@ -66,7 +66,7 @@ export class MapiTypeConverter {
         var clsidConverter = new MapiTypeConverterMapEntry(
             MapiTypeConverterTypeSystem.guid,
             (s) => new Guid(s),             //Parse
-            (o) => (<Guid>o).ToString()     //ConvertToString
+            (o) => (<Guid>o).toString()     //ConvertToString
             );
 
         map.Add(
@@ -76,7 +76,7 @@ export class MapiTypeConverter {
         var clsidArrayConverter = new MapiTypeConverterMapEntry(
             MapiTypeConverterTypeSystem.guid,
             (s) => new Guid(s),             //Parse
-            (o) => (<Guid>o).ToString(),    //ConvertToString
+            (o) => (<Guid>o).toString(),    //ConvertToString
             true                            //IsArray
             );
 
@@ -297,4 +297,4 @@ export class MapiTypeConverter {
         }
         return num;
     }
-}   
\ No newline at end of file
+}