diff --git a/solr/CHANGES.txt b/solr/CHANGES.txt
index 2f4827b2294..b693543c1c0 100644
--- a/solr/CHANGES.txt
+++ b/solr/CHANGES.txt
@@ -214,6 +214,9 @@ Bug Fixes
 * SOLR-9441: Solr collection backup on HDFS can only be manipulated by the Solr process owner. 
  (Hrishikesh Gadre via Mark Miller)
 
+* SOLR-9536: OldBackupDirectory timestamp field needs to be initialized to avoid NPE.
+ (Hrishikesh Gadre via Mark Miller)
+ 
 Optimizations
 ----------------------
 
diff --git a/solr/core/src/java/org/apache/solr/handler/OldBackupDirectory.java b/solr/core/src/java/org/apache/solr/handler/OldBackupDirectory.java
index 2b19116c926..79c5f09f7e9 100644
--- a/solr/core/src/java/org/apache/solr/handler/OldBackupDirectory.java
+++ b/solr/core/src/java/org/apache/solr/handler/OldBackupDirectory.java
@@ -32,7 +32,7 @@ class OldBackupDirectory implements Comparable<OldBackupDirectory> {
 
   private URI basePath;
   private String dirName;
-  private Optional<Date> timestamp;
+  private Optional<Date> timestamp = Optional.empty();
 
   public OldBackupDirectory(URI basePath, String dirName) {
     this.dirName = Preconditions.checkNotNull(dirName);