diff --git a/changelog.html b/changelog.html
index 721f5e71e5..154d84209c 100644
--- a/changelog.html
+++ b/changelog.html
@@ -63,6 +63,9 @@ Upcoming changes</a>
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-22262">issue 22262</a>)
   <li class=bug>
     <code>identity.key</code>, used to secure some communications with Jenkins, now stored encrypted with the master key.
+  <li class=bug>
+    When dynamically loading a plugin which another loaded plugin already had an optional dependency on, class loading errors could result before restart.
+    (<a href="https://issues.jenkins-ci.org/browse/JENKINS-19976">issue 19976</a>)
   <li class=bug>
     Memory leaks in the old data monitor.
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-19544">issue 19544</a>)
diff --git a/core/src/main/java/hudson/ClassicPluginStrategy.java b/core/src/main/java/hudson/ClassicPluginStrategy.java
index 18cbb3e0fa..f321605afe 100644
--- a/core/src/main/java/hudson/ClassicPluginStrategy.java
+++ b/core/src/main/java/hudson/ClassicPluginStrategy.java
@@ -377,15 +377,6 @@ public class ClassicPluginStrategy implements PluginStrategy {
         plugin.getPlugin().start();
     }
 
-    /**
-     * Called when a plugin is deployed, and there is a plugin optionally depending on that plugin.
-     * The class loader of the existing depending plugin should be updated
-     * to load classes from the newly deployed plugin.
-     * 
-     * @param depender the plugin to update its class loader
-     * @param dependee
-     * @see hudson.PluginStrategy#updateDependency(hudson.PluginWrapper, hudson.PluginWrapper)
-     */
     @Override
     public void updateDependency(PluginWrapper depender, PluginWrapper dependee) {
         DependencyClassLoader classLoader = findAncestorDependencyClassLoader(depender.classLoader);
diff --git a/core/src/main/java/hudson/PluginManager.java b/core/src/main/java/hudson/PluginManager.java
index d77f12087d..17900b6309 100644
--- a/core/src/main/java/hudson/PluginManager.java
+++ b/core/src/main/java/hudson/PluginManager.java
@@ -464,7 +464,11 @@ public abstract class PluginManager extends AbstractModelObject implements OnMas
                 if (d.shortName.equals(p.getShortName())) {
                     // this plugin depends on the newly loaded one!
                     // recalculate dependencies!
-                    getPluginStrategy().updateDependency(depender, p);
+                    try {
+                        getPluginStrategy().updateDependency(depender, p);
+                    } catch (AbstractMethodError x) {
+                        LOGGER.log(WARNING, "{0} does not yet implement updateDependency", getPluginStrategy().getClass());
+                    }
                     break;
                 }
             }
diff --git a/core/src/main/java/hudson/PluginStrategy.java b/core/src/main/java/hudson/PluginStrategy.java
index d61e23732a..e599812e4a 100644
--- a/core/src/main/java/hudson/PluginStrategy.java
+++ b/core/src/main/java/hudson/PluginStrategy.java
@@ -79,10 +79,12 @@ public interface PluginStrategy extends ExtensionPoint {
 	<T> List<ExtensionComponent<T>> findComponents(Class<T> type, Hudson hudson);
     
     /**
-     * Called when a plugin that is depended by another plugin is newly deployed.
-     * 
+     * Called when a plugin is installed, but there was already a plugin installed which optionally depended on that plugin.
+     * The class loader of the existing depending plugin should be updated
+     * to load classes from the newly installed plugin.
      * @param depender plugin depending on dependee.
      * @param dependee newly loaded plugin.
+     * @since 1.557
      */
     void updateDependency(PluginWrapper depender, PluginWrapper dependee);
 }
diff --git a/test/src/test/java/hudson/PluginManagerTest.java b/test/src/test/java/hudson/PluginManagerTest.java
index b068598c94..4f50aec47f 100644
--- a/test/src/test/java/hudson/PluginManagerTest.java
+++ b/test/src/test/java/hudson/PluginManagerTest.java
@@ -33,13 +33,6 @@ import hudson.model.UpdateSite;
 import hudson.scm.SubversionSCM;
 import hudson.util.FormValidation;
 import hudson.util.PersistedList;
-import org.apache.commons.io.FileUtils;
-import org.apache.tools.ant.filters.StringInputStream;
-import org.jvnet.hudson.test.HudsonTestCase;
-import org.jvnet.hudson.test.Url;
-import org.jvnet.hudson.test.recipes.WithPlugin;
-import org.jvnet.hudson.test.recipes.WithPluginManager;
-
 import java.io.File;
 import java.lang.reflect.Method;
 import java.net.URL;
@@ -47,6 +40,13 @@ import java.net.URLClassLoader;
 import java.util.Collections;
 import java.util.List;
 import java.util.concurrent.Future;
+import org.apache.commons.io.FileUtils;
+import org.apache.tools.ant.filters.StringInputStream;
+import org.jvnet.hudson.test.Bug;
+import org.jvnet.hudson.test.HudsonTestCase;
+import org.jvnet.hudson.test.Url;
+import org.jvnet.hudson.test.recipes.WithPlugin;
+import org.jvnet.hudson.test.recipes.WithPluginManager;
 
 /**
  * @author Kohsuke Kawaguchi
@@ -310,6 +310,7 @@ public class PluginManagerTest extends HudsonTestCase {
      * 
      * @throws Exception
      */
+    @Bug(19976)
     public void testInstallDependedPluginWithoutRestart() throws Exception {
         // Load depender.
         {