--- a/src/java.base/share/classes/java/lang/Class.java	Mon Jan 14 11:22:32 2019 -0800
+++ b/src/java.base/share/classes/java/lang/Class.java	Mon Jan 14 23:05:26 2019 +0100
@@ -3419,8 +3419,8 @@
         StringBuilder sb = new StringBuilder();
         sb.append(getName() + "." + name + "(");
         if (argTypes != null) {
-            Stream.of(argTypes).map(c -> {return (c == null) ? "null" : c.getName();}).
-                collect(Collectors.joining(","));
+            sb.append(Stream.of(argTypes).map(c -> {return (c == null) ? "null" : c.getName();}).
+                      collect(Collectors.joining(",")));
         }
         sb.append(")");
         return sb.toString();