diff --git a/lib/webrick/httpproxy.rb b/lib/webrick/httpproxy.rb
index 65f830ecbb..c5ed44f1da 100644
--- a/lib/webrick/httpproxy.rb
+++ b/lib/webrick/httpproxy.rb
@@ -110,7 +110,7 @@ module WEBrick
         proxy_host = proxy.host
         proxy_port = proxy.port
         if proxy.userinfo
-          credentials = "Basic " + encode64(proxy.userinfo)
+          credentials = "Basic " + [proxy.userinfo].pack("m*")
           header['proxy-authorization'] = credentials
         end
       end
@@ -170,7 +170,7 @@ module WEBrick
       if proxy = proxy_uri(req, res)
         proxy_request_line = "CONNECT #{host}:#{port} HTTP/1.0"
         if proxy.userinfo
-          credentials = "Basic " + encode64(proxy.userinfo)
+          credentials = "Basic " + [proxy.userinfo].pack("m*")
         end
         host, port = proxy.host, proxy.port
       end