diff --git a/lib/writeexcel/workbook.rb b/lib/writeexcel/workbook.rb
index <HASH>..<HASH> 100644
--- a/lib/writeexcel/workbook.rb
+++ b/lib/writeexcel/workbook.rb
@@ -2972,8 +2972,8 @@ class Workbook < BIFFWriter
     end
 
     # Change length field of the first MSODRAWINGGROUP block. Case 2 and 3.
-    tmp = data.dup
-    tmp[0, limit + 4] = ""
+    tmp = data[0, limit + 4]
+    data[0, limit + 4] = ""
     tmp[2, 2] = [limit].pack('v')
     append(tmp)
* bug fix: endless loop when image size > <I>

  in add_mso_drawing_group_continue(data)
  this bug was found by Kyle's mail. thanks Kyle.