--- a/src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/formats/html/HtmlDocletWriter.java	Thu Jun 06 10:01:36 2019 -0700
+++ b/src/jdk.javadoc/share/classes/jdk/javadoc/internal/doclets/formats/html/HtmlDocletWriter.java	Thu Jun 06 10:36:43 2019 -0700
@@ -27,6 +27,7 @@
 
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.ListIterator;
@@ -197,6 +198,14 @@
     protected Script mainBodyScript;
 
     /**
+     * A table of the anchors used for at-index and related tags,
+     * so that they can be made unique by appending a suitable suffix.
+     * (Ideally, javadoc should be tracking all id's generated in a file
+     * to avoid generating duplicates.)
+     */
+    Map<String, Integer> indexAnchorTable = new HashMap<>();
+
+    /**
      * Constructor to construct the HtmlStandardWriter object.
      *
      * @param configuration the configuration for this doclet