diff --git a/lib/coderay/encoders/encoder.rb b/lib/coderay/encoders/encoder.rb
index fa5695d6..2baeedb6 100644
--- a/lib/coderay/encoders/encoder.rb
+++ b/lib/coderay/encoders/encoder.rb
@@ -146,7 +146,7 @@ def setup options
       end
       
       def get_output options
-        options[:out] || ''
+        options[:out] || ''.dup
       end
       
       # Append data.to_s to the output. Returns the argument.
diff --git a/lib/coderay/encoders/html.rb b/lib/coderay/encoders/html.rb
index 942b9c89..1b33e921 100644
--- a/lib/coderay/encoders/html.rb
+++ b/lib/coderay/encoders/html.rb
@@ -176,7 +176,7 @@ def setup options
       
       if options[:wrap] || options[:line_numbers]
         @real_out = @out
-        @out = ''
+        @out = ''.dup
       end
       
       @break_lines = (options[:break_lines] == true)
@@ -314,7 +314,7 @@ def check_group_nesting name, kind
     end
     
     def break_lines text, style
-      reopen = ''
+      reopen = ''.dup
       @opened.each_with_index do |kind, index|
         reopen << (@span_for_kinds[index > 0 ? [kind, *@opened[0...index]] : kind] || '<span>')
       end