diff --git a/src/java.base/share/classes/java/nio/channels/FileChannel.java b/src/java.base/share/classes/java/nio/channels/FileChannel.java
index 5d8af5239c0..b4cc05441d9 100644
--- a/src/java.base/share/classes/java/nio/channels/FileChannel.java
+++ b/src/java.base/share/classes/java/nio/channels/FileChannel.java
@@ -997,6 +997,9 @@ public abstract class FileChannel
      *           of mapped memory associated with the returned mapped memory
      *           segment is unspecified and should not be relied upon.
      *
+     * @implSpec The default implementation of this method throws
+     *           {@code UnsupportedOperationException}.
+     *
      * @param   mode
      *          The file mapping mode, see
      *          {@link FileChannel#map(FileChannel.MapMode, long, long)};