diff --git a/lib/email/message_builder.rb b/lib/email/message_builder.rb
index e376450f1..3d0687ee0 100644
--- a/lib/email/message_builder.rb
+++ b/lib/email/message_builder.rb
@@ -87,7 +87,7 @@ module Email
           value = header[1].strip
           result[name] = value if name.length > 0 && value.length > 0
         end
-      } if !string.nil?
+      } unless string.nil?
       result
     end