diff --git a/lib/net/http/generic_request.rb b/lib/net/http/generic_request.rb
index e8525b3..20afb3f 100644
--- a/lib/net/http/generic_request.rb
+++ b/lib/net/http/generic_request.rb
@@ -99,7 +99,9 @@ class Net::HTTPGenericRequest
   #
 
   def exec(sock, ver, path)   #:nodoc: internal use only
-    self['host'] = "#{@uri.host}:#{@uri.port}" if @uri
+    if @uri && @uri.port != @uri.default_port
+      self['host'] = "#{@uri.host}:#{@uri.port}"
+    end
 
     if @body
       send_request_with_body sock, ver, path, @body