diff --git a/core/src/main/java/hudson/PluginManager.java b/core/src/main/java/hudson/PluginManager.java
index d067ed49fe..7dad538d6f 100644
--- a/core/src/main/java/hudson/PluginManager.java
+++ b/core/src/main/java/hudson/PluginManager.java
@@ -911,9 +911,7 @@ public abstract class PluginManager extends AbstractModelObject implements OnMas
             plugins.add(p);
             if (p.isActive())
                 activePlugins.add(p);
-            synchronized (((UberClassLoader) uberClassLoader).loaded) {
-                ((UberClassLoader) uberClassLoader).loaded.clear();
-            }
+            ((UberClassLoader) uberClassLoader).loaded.clear();
 
             // TODO antimodular; perhaps should have a PluginListener to complement ExtensionListListener?
             CustomClassFilter.Contributed.load();
diff --git a/src/spotbugs/spotbugs-excludes.xml b/src/spotbugs/spotbugs-excludes.xml
index ccd7c6f5c7..b825555ade 100644
--- a/src/spotbugs/spotbugs-excludes.xml
+++ b/src/spotbugs/spotbugs-excludes.xml
@@ -228,10 +228,6 @@
           <Class name="hudson.model.ListView$Listener"/>
         </Or>
       </And>
-      <And>
-        <Bug pattern="JLM_JSR166_UTILCONCURRENT_MONITORENTER"/>
-        <Class name="hudson.PluginManager"/>
-      </And>
       <And>
         <Bug pattern="LI_LAZY_INIT_STATIC"/>
         <Or>