diff -r 4b273ed9a82d -r 9637557def32 src/hotspot/share/runtime/arguments.cpp
--- a/src/hotspot/share/runtime/arguments.cpp	Tue Feb 27 21:29:19 2018 -0800
+++ b/src/hotspot/share/runtime/arguments.cpp	Wed Feb 28 09:30:06 2018 +0100
@@ -3096,7 +3096,8 @@
     } else if (match_option(option, "-Xlog", &tail)) {
       bool ret = false;
       if (strcmp(tail, ":help") == 0) {
-        LogConfiguration::print_command_line_help(defaultStream::output_stream());
+        fileStream stream(defaultStream::output_stream());
+        LogConfiguration::print_command_line_help(&stream);
         vm_exit(0);
       } else if (strcmp(tail, ":disable") == 0) {
         LogConfiguration::disable_logging();
@@ -3109,7 +3110,7 @@
       }
       if (ret == false) {
         jio_fprintf(defaultStream::error_stream(),
-                    "Invalid -Xlog option '-Xlog%s'\n",
+                    "Invalid -Xlog option '-Xlog%s', see error log for details.\n",
                     tail);
         return JNI_EINVAL;
       }