diff --git a/lib/mail/header.rb b/lib/mail/header.rb
index 1ef4cbae7..3d81f2a2e 100644
--- a/lib/mail/header.rb
+++ b/lib/mail/header.rb
@@ -159,15 +159,15 @@ def []=(name, value)
         # Need to insert in correct order for trace fields
         self.fields << Field.new(name.to_s, value, charset)
       end
+      if dasherize(fn) == "content-type"
+        # Update charset if specified in Content-Type
+        params = self[:content_type].parameters rescue nil
+        @charset = params && params[:charset]
+      end
     end
     
     def charset
-      params = self[:content_type].parameters rescue nil
-      if params
-        params[:charset]
-      else
-        @charset
-      end
+      @charset
     end
     
     def charset=(val)