Replacing old block with new one.

lib/annotate/annotate_models.rb

@@ -241,13 +241,17 @@ module AnnotateModels
 #           end
 # =======
 
-          # Strip the old schema info, and insert new schema info.
-          old_content.sub!(encoding, '')
-          old_content.sub!(PATTERN, '')
-
-          new_content = options[position].to_s == 'after' ?
-            (encoding_header + (old_content.rstrip + "\n\n" + info_block)) :
-            (encoding_header + info_block + "\n" + old_content)
+          if PATTERN.match(old_content)
+            new_content = old_content.sub(PATTERN, info_block)
+          else
+            # Strip the old schema info, and insert new schema info.
+            old_content.sub!(encoding, '')
+            old_content.sub!(PATTERN, '')
+
+            new_content = options[position].to_s == 'after' ?
+              (encoding_header + (old_content.rstrip + "\n\n" + info_block)) :
+              (encoding_header + info_block + "\n" + old_content)
+          end
 
           File.open(file_name, "wb") { |f| f.puts new_content }
           return true