diff -r 88502b1cf76f -r 7799a51dbe30 test/langtools/tools/javac/patterns/UncheckedWarningOnMatchesTest.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/langtools/tools/javac/patterns/UncheckedWarningOnMatchesTest.java	Wed Nov 27 09:00:01 2019 +0100
@@ -0,0 +1,18 @@
+/*
+ * @test /nodynamiccopyright/
+ * @bug 8187429 8231827
+ * @summary Missing unchecked conversion warning
+ * @compile/fail/ref=UncheckedWarningOnMatchesTest.out -Xlint:unchecked -Werror -XDrawDiagnostics --enable-preview -source ${jdk.version} UncheckedWarningOnMatchesTest.java
+ */
+import java.util.ArrayList;
+
+public class UncheckedWarningOnMatchesTest {
+
+    public static void main(String [] args) {
+
+        Object o = new ArrayList<UncheckedWarningOnMatchesTest>();
+        if (o instanceof ArrayList<Integer> ai) {  // unchecked conversion
+            System.out.println("Blah");
+        }
+    }
+}