diff --git a/main/POIFS/NIO/FileBackedDataSource.cs b/main/POIFS/NIO/FileBackedDataSource.cs
index 2219e4d24..92fc61971 100644
--- a/main/POIFS/NIO/FileBackedDataSource.cs
+++ b/main/POIFS/NIO/FileBackedDataSource.cs
@@ -169,7 +169,8 @@ public override void CopyTo(Stream stream)
         {
             //byte[] tempBuffer = new byte[stream.Length];
             //fileStream.Read(tempBuffer, 0, tempBuffer.Length);
-            stream.Write(fileStream.GetBuffer(), 0, (int)fileStream.Length);        }
+            byte[] tempBuffer = fileStream.ToArray();
+            stream.Write(tempBuffer, 0, tempBuffer.Length);        }
 
         public override long Size
         {