--- a/src/java.base/share/classes/java/lang/module/Configuration.java	Tue Sep 11 13:54:34 2018 -0700
+++ b/src/java.base/share/classes/java/lang/module/Configuration.java	Tue Sep 11 14:51:45 2018 -0700
@@ -601,8 +601,7 @@
                 // push in reverse order
                 for (int i = layer.parents.size() - 1; i >= 0; i--) {
                     Configuration parent = layer.parents.get(i);
-                    if (!visited.contains(parent)) {
-                        visited.add(parent);
+                    if (visited.add(parent)) {
                         stack.push(parent);
                     }
                 }