diff --git a/lib/haml/temple_engine.rb b/lib/haml/temple_engine.rb
index 915c7582ff..3a10bf5888 100644
--- a/lib/haml/temple_engine.rb
+++ b/lib/haml/temple_engine.rb
@@ -54,7 +54,7 @@ def precompiled
     end
 
     def precompiled_with_return_value
-      "#{precompiled};#{precompiled_method_return_value}"
+      "#{precompiled};#{precompiled_method_return_value}".dup
     end
 
     # The source code that is evaluated to produce the Haml document.
@@ -77,7 +77,7 @@ def precompiled_with_ambles(local_names, after_preamble: '')
 @haml_buffer = @haml_buffer.upper if @haml_buffer
 end
 END
-      "#{preamble}#{locals_code(local_names)}#{precompiled}#{postamble}"
+      "#{preamble}#{locals_code(local_names)}#{precompiled}#{postamble}".dup
     end
 
     private