diff --git a/lib/register/assembler.rb b/lib/register/assembler.rb
index 0048ebed..a9d94a8d 100644
--- a/lib/register/assembler.rb
+++ b/lib/register/assembler.rb
@@ -241,7 +241,7 @@ module Register
     end
 
     def pad_to length
-      length += length + 2 # for header, type and layout
+      length += 2 # for header, type and layout
       pad = padded(length) - length
       pad.times do
         @stream.write_uint32(0)