diff --git a/lib/uri/rfc3986_parser.rb b/lib/uri/rfc3986_parser.rb
index 41fbea4b03..092a1ac89d 100644
--- a/lib/uri/rfc3986_parser.rb
+++ b/lib/uri/rfc3986_parser.rb
@@ -164,7 +164,7 @@ module URI
         QUERY: %r[\A(?:%\h\h|[!$&-.0-9:;=@A-Z_a-z~/?])*+\z],
         FRAGMENT: %r[\A#{FRAGMENT}\z]o,
         OPAQUE: %r[\A(?:[^/].*)?\z],
-        PORT: /\A[\x09\x0a\x0c\x0d ]*\d*[\x09\x0a\x0c\x0d ]*\z/,
+        PORT: /\A[\x09\x0a\x0c\x0d ]*+\d*[\x09\x0a\x0c\x0d ]*\z/,
       }
     end
 
diff --git a/test/uri/test_parser.rb b/test/uri/test_parser.rb
index 55abe2c583..75c02fe65b 100644
--- a/test/uri/test_parser.rb
+++ b/test/uri/test_parser.rb
@@ -99,4 +99,14 @@ class URI::TestParser < Test::Unit::TestCase
       end
     end
   end
+
+  def test_rfc3986_port_check
+    pre = ->(length) {"\t" * length + "a"}
+    uri = URI.parse("http://my.example.com")
+    assert_linear_performance((1..5).map {|i| 10**i}, pre: pre) do |port|
+      assert_raise(URI::InvalidComponentError) do
+        uri.port = port
+      end
+    end
+  end
 end