diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index 83bd5ad1a4b..8677c6e7861 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -70,6 +70,9 @@ Bug Fixes
 * LUCENE-6730: Hyper-parameter c is ignored in term frequency NormalizationH1.
   (Ahmet Arslan via Robert Muir)
 
+* LUCENE-6618: Properly set MMapDirectory.UNMAP_SUPPORTED when it is now allowed
+  by security policy. (Robert Muir)
+
 Other
 
 * LUCENE-6174: Improve "ant eclipse" to select right JRE for building.
diff --git a/lucene/core/src/java/org/apache/lucene/store/MMapDirectory.java b/lucene/core/src/java/org/apache/lucene/store/MMapDirectory.java
index 4d828a603cf..65486d41d77 100644
--- a/lucene/core/src/java/org/apache/lucene/store/MMapDirectory.java
+++ b/lucene/core/src/java/org/apache/lucene/store/MMapDirectory.java
@@ -167,7 +167,9 @@ public class MMapDirectory extends FSDirectory {
   
   private static boolean checkUnmapSupported() {
     try {
-      Class.forName("java.nio.DirectByteBuffer").getMethod("cleaner");
+      Class<?> clazz = Class.forName("java.nio.DirectByteBuffer");
+      Method method = clazz.getMethod("cleaner");
+      method.setAccessible(true);
       return true;
     } catch (Exception e) {
       return false;