diff --git a/lib/serenity/escape_xml.rb b/lib/serenity/escape_xml.rb
index 49d84b8..aeeb9cf 100644
--- a/lib/serenity/escape_xml.rb
+++ b/lib/serenity/escape_xml.rb
@@ -4,14 +4,18 @@ def escape_xml
   end
 
   def convert_newlines
-    gsub!("\n", '<text:line-break/>')
+    if not self.frozen?
+      gsub!("\n", '<text:line-break/>')
+    end
     self
   end
 
   def mgsub!(key_value_pairs=[].freeze)
     regexp_fragments = key_value_pairs.collect { |k,v| k }
-    gsub!(Regexp.union(*regexp_fragments)) do |match|
-      key_value_pairs.detect{|k,v| k =~ match}[1]
+    if not self.frozen?
+      gsub!(Regexp.union(*regexp_fragments)) do |match|
+        key_value_pairs.detect{|k,v| k =~ match}[1]
+      end
     end
     self
   end