diff --git a/lib/rexml/doctype.rb b/lib/rexml/doctype.rb
index 678095a..3928675 100644
--- a/lib/rexml/doctype.rb
+++ b/lib/rexml/doctype.rb
@@ -251,7 +251,7 @@ module REXML
       "<!NOTATION #@name #@middle#{
         @public ? ' ' + public.inspect : ''
       }#{
-        @system ? ' ' +@system.inspect : ''
+        @system ? ' ' + @system.inspect : ''
       }>"
     end