diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index 89d4ed02441..e188a1985e4 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -392,6 +392,9 @@ Release 2.4.0 - UNRELEASED
     HDFS-5908. Change AclFeature to capture list of ACL entries in an
     ImmutableList. (cnauroth)
 
+    HDFS-6028. Print clearer error message when user attempts to delete required
+    mask entry from ACL. (cnauroth)
+
 Release 2.3.1 - UNRELEASED
 
   INCOMPATIBLE CHANGES
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/AclTransformation.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/AclTransformation.java
index 44a2f3dd118..3a3f9206ebd 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/AclTransformation.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/AclTransformation.java
@@ -365,7 +365,7 @@ final class AclTransformation {
           maskDirty.contains(scope)) {
         // Caller explicitly removed mask entry, but it's required.
         throw new AclException(
-          "Invalid ACL: mask is required, but it was deleted.");
+          "Invalid ACL: mask is required and cannot be deleted.");
       } else if (providedMask.containsKey(scope) &&
           (!scopeDirty.contains(scope) || maskDirty.contains(scope))) {
         // Caller explicitly provided new mask, or we are preserving the existing