diff -r 88502b1cf76f -r 7799a51dbe30 test/langtools/tools/javac/patterns/DuplicateBindingTest.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/langtools/tools/javac/patterns/DuplicateBindingTest.java	Wed Nov 27 09:00:01 2019 +0100
@@ -0,0 +1,22 @@
+/*
+ * @test /nodynamiccopyright/
+ * @bug 8231827
+ * @summary Basic pattern bindings scope test
+ * @compile/fail/ref=DuplicateBindingTest.out -XDrawDiagnostics --enable-preview -source ${jdk.version} DuplicateBindingTest.java
+ */
+
+public class DuplicateBindingTest {
+
+    int f;
+
+    public static void main(String[] args) {
+
+        if (args != null) {
+            int s;
+            if (args[0] instanceof String s) { // NOT OK. Redef same scope.
+            }
+            if (args[0] instanceof String f) { // OK to redef field.
+            }
+        }
+    }
+}