diff --git a/lib/net/http/header.rb b/lib/net/http/header.rb
index 1f795d7d9d..b20894d66a 100644
--- a/lib/net/http/header.rb
+++ b/lib/net/http/header.rb
@@ -362,16 +362,18 @@ def content_type
   # Returns a content type string such as "text".
   # This method returns nil if Content-Type: header field does not exist.
   def main_type
-    return nil unless @header['content-type']
-    self['Content-Type'].split(';').first.to_s.split('/')[0].to_s.strip
+    values = @header['content-type']
+    return nil unless values
+    values.first.split(';').first.to_s.split('/')[0].to_s.strip
   end
 
   # Returns a content type string such as "html".
   # This method returns nil if Content-Type: header field does not exist
   # or sub-type is not given (e.g. "Content-Type: text").
   def sub_type
-    return nil unless @header['content-type']
-    _, sub = *self['Content-Type'].split(';').first.to_s.split('/')
+    values = @header['content-type']
+    return nil unless values
+    _, sub = *values.first.split(';').first.to_s.split('/')
     return nil unless sub
     sub.strip
   end