--- a/src/java.base/share/classes/java/nio/MappedByteBuffer.java	Mon Feb 12 16:36:15 2018 +0100
+++ b/src/java.base/share/classes/java/nio/MappedByteBuffer.java	Mon Feb 12 08:19:23 2018 -0800
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -90,12 +90,6 @@
         this.fd = null;
     }
 
-    private void checkMapped() {
-        if (fd == null)
-            // Can only happen if a luser explicitly casts a direct byte buffer
-            throw new UnsupportedOperationException();
-    }
-
     // Returns the distance (in bytes) of the buffer from the page aligned address
     // of the mapping. Computed each time to avoid storing in every direct buffer.
     private long mappingOffset() {
@@ -131,7 +125,9 @@
      *          is resident in physical memory
      */
     public final boolean isLoaded() {
-        checkMapped();
+        if (fd == null) {
+            return true;
+        }
         if ((address == 0) || (capacity() == 0))
             return true;
         long offset = mappingOffset();
@@ -153,7 +149,9 @@
      * @return  This buffer
      */
     public final MappedByteBuffer load() {
-        checkMapped();
+        if (fd == null) {
+            return this;
+        }
         if ((address == 0) || (capacity() == 0))
             return this;
         long offset = mappingOffset();
@@ -197,7 +195,9 @@
      * @return  This buffer
      */
     public final MappedByteBuffer force() {
-        checkMapped();
+        if (fd == null) {
+            return this;
+        }
         if ((address != 0) && (capacity() != 0)) {
             long offset = mappingOffset();
             force0(fd, mappingAddress(offset), mappingLength(offset));

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/jdk/java/nio/MappedByteBuffer/SubclassCastUOE.java	Mon Feb 12 08:19:23 2018 -0800
@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/* @test
+ * @bug 8191416
+ * @summary Verify no UnsupportedOperationException for cast subclass
+ */
+
+import java.nio.ByteBuffer;
+import java.nio.MappedByteBuffer;
+
+public class SubclassCastUOE {
+    public static void main(String[] args) throws Exception {
+        ByteBuffer buf = ByteBuffer.allocateDirect(37);
+
+        if (!(buf instanceof MappedByteBuffer)) {
+            throw new RuntimeException("Direct buffer not a MappedByteBuffer");
+        }
+
+        if (((MappedByteBuffer)buf).load() != buf) {
+            throw new RuntimeException("load() did not return same buffer");
+        }
+
+        if (!((MappedByteBuffer)buf).isLoaded()) {
+            throw new RuntimeException("isLoaded() returned false");
+        }
+
+        if (((MappedByteBuffer)buf).force() != buf) {
+            throw new RuntimeException("force() did not return same buffer");
+        }
+    }
+}