diff --git a/changelog.html b/changelog.html
index 9b55d39fb34b2184839c44c99d8be81d78397ae4..d8754a7fe4e50343de9061b34a88d4ef8f3b44be 100644
--- a/changelog.html
+++ b/changelog.html
@@ -58,6 +58,9 @@ Upcoming changes</a>
   <li class=rfe>
     Added 'no-store' to the 'Cache-Control' header to avoid accidental information leak through local cache backup
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-24337">issue 24337</a>)
+  <li class=bug>
+    Deadlock in <code>OldDataMonitor</code>.
+    (<a href="https://issues.jenkins-ci.org/browse/JENKINS-24358">issue 24358</a>)
 </ul>
 </div><!--=TRUNK-END=-->
 
diff --git a/core/src/main/java/hudson/diagnosis/OldDataMonitor.java b/core/src/main/java/hudson/diagnosis/OldDataMonitor.java
index b9e18d1b689d04f7d376293b7c0110c16019c81f..cb6e890e60ae5a266b49c0298831d5ccd029d0fc 100644
--- a/core/src/main/java/hudson/diagnosis/OldDataMonitor.java
+++ b/core/src/main/java/hudson/diagnosis/OldDataMonitor.java
@@ -84,9 +84,13 @@ public class OldDataMonitor extends AdministrativeMonitor {
         return !data.isEmpty();
     }
 
-    public synchronized Map<Saveable,VersionRange> getData() {
+    public Map<Saveable,VersionRange> getData() {
+        Map<SaveableReference,VersionRange> _data;
+        synchronized (this) {
+            _data = new HashMap<SaveableReference,VersionRange>(this.data);
+        }
         Map<Saveable,VersionRange> r = new HashMap<Saveable,VersionRange>();
-        for (Map.Entry<SaveableReference,VersionRange> entry : data.entrySet()) {
+        for (Map.Entry<SaveableReference,VersionRange> entry : _data.entrySet()) {
             Saveable s = entry.getKey().get();
             if (s != null) {
                 r.put(s, entry.getValue());