diff --git a/source/System/Text/StringBuilder.cs b/source/System/Text/StringBuilder.cs
index 2b8a85ea..1bd9fdbb 100644
--- a/source/System/Text/StringBuilder.cs
+++ b/source/System/Text/StringBuilder.cs
@@ -190,7 +190,7 @@ public unsafe StringBuilder(string value, int startIndex, int length, int capaci
             //Set the length of the chunk
             _chunkLength = length;
             //Copy the value to the chunkChars
-            value.ToCharArray().CopyTo(_chunkChars, 0);
+            value.ToCharArray(startIndex, length).CopyTo(_chunkChars, 0);
         }
 
         private StringBuilder(int size, int maxCapacity, StringBuilder previousBlock)