diff --git a/lib/uri/generic.rb b/lib/uri/generic.rb
index f3540a24bb..9ea2335cea 100644
--- a/lib/uri/generic.rb
+++ b/lib/uri/generic.rb
@@ -1364,6 +1364,9 @@ module URI
           str << ':'
           str << @port.to_s
         end
+        if (@host || @port) && !@path.empty? && !@path.start_with?('/')
+          str << '/'
+        end
         str << @path
         if @query
           str << '?'
diff --git a/test/uri/test_generic.rb b/test/uri/test_generic.rb
index e6619373c6..8209363b82 100644
--- a/test/uri/test_generic.rb
+++ b/test/uri/test_generic.rb
@@ -26,6 +26,17 @@ class URI::TestGeneric < Test::Unit::TestCase
     assert_equal "postgres:///foo", URI("postgres:///foo").to_s
     assert_equal "http:///foo", URI("http:///foo").to_s
     assert_equal "http:/foo", URI("http:/foo").to_s
+
+    uri = URI('rel_path')
+    assert_equal "rel_path", uri.to_s
+    uri.scheme = 'http'
+    assert_equal "http:rel_path", uri.to_s
+    uri.host = 'h'
+    assert_equal "http://h/rel_path", uri.to_s
+    uri.port = 8080
+    assert_equal "http://h:8080/rel_path", uri.to_s
+    uri.host = nil
+    assert_equal "http::8080/rel_path", uri.to_s
   end
 
   def test_parse