--- log4j-core/src/main/java/org/apache/logging/log4j/core/appender/AbstractOutputStreamAppender.java.orig	2015-01-13 21:38:15.521106298 +0000
+++ log4j-core/src/main/java/org/apache/logging/log4j/core/appender/AbstractOutputStreamAppender.java	2015-01-13 21:39:29.798590605 +0000
@@ -48,8 +48,8 @@
     private final M manager;
 
     private final ReadWriteLock rwLock = new ReentrantReadWriteLock();
-    private final Lock readLock = rwLock.readLock();
-    
+    private final Lock writeLock = rwLock.writeLock();
+
     /**
      * Instantiate a WriterAppender and set the output destination to a
      * new {@link java.io.OutputStreamWriter} initialized with <code>os</code>
@@ -103,7 +103,7 @@
      */
     @Override
     public void append(final LogEvent event) {
-        readLock.lock();
+        writeLock.lock();
         try {
             final byte[] bytes = getLayout().toByteArray(event);
             if (bytes.length > 0) {
@@ -116,7 +116,7 @@
             error("Unable to write to stream " + manager.getName() + " for appender " + getName());
             throw ex;
         } finally {
-            readLock.unlock();
+            writeLock.unlock();
         }
     }
 }
--- log4j-core/src/test/java/org/apache/logging/log4j/core/appender/SyslogAppenderTest.java.orig	2015-01-13 21:39:08.686168687 +0000
+++ log4j-core/src/test/java/org/apache/logging/log4j/core/appender/SyslogAppenderTest.java	2015-01-13 21:39:29.798590605 +0000
@@ -18,6 +18,7 @@
 
 import java.io.IOException;
 import java.net.SocketException;
+import java.util.ArrayList;
 
 import org.apache.logging.log4j.core.net.Facility;
 import org.apache.logging.log4j.core.net.mock.MockSyslogServerFactory;
@@ -78,6 +79,31 @@
         root.removeAppender(appender);
         appender.stop();
     }
+
+    @Test
+    public void testUDPAppenderInParallel() throws Exception {
+        initUDPTestEnvironment("bsd");
+
+        ArrayList<Thread> threads = new ArrayList<Thread>();
+        for (int i = 0; i < 1000; i++) {
+          Thread thread = new Thread(new Runnable() {
+            public void run() {
+              sendLegacyBSDMessage("This is a test message");
+            }
+          });
+          threads.add(thread);
+        }
+        for (Thread thread : threads) {
+          thread.start();
+        }
+        for (Thread thread : threads) {
+          thread.join();
+        }
+        checkTheNumberOfSentAndReceivedMessages();
+
+        root.removeAppender(appender);
+        appender.stop();
+    }
 
     @Test
     public void testUDPStructuredAppender() throws Exception {
--- log4j-core/src/test/java/org/apache/logging/log4j/core/appender/SyslogAppenderTestBase.java.orig	2015-01-13 21:39:21.022415215 +0000
+++ log4j-core/src/test/java/org/apache/logging/log4j/core/appender/SyslogAppenderTestBase.java	2015-01-13 21:39:29.802590684 +0000
@@ -17,6 +17,7 @@
 package org.apache.logging.log4j.core.appender;
 
 import java.util.ArrayList;
+import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
@@ -45,7 +46,7 @@
     protected MockSyslogServer syslogServer;
     protected SyslogAppender appender;
     protected Logger root = ctx.getLogger("SyslogAppenderTest");
-    protected List<String> sentMessages = new ArrayList<String>();
+    protected List<String> sentMessages = new CopyOnWriteArrayList<String>();
     protected boolean includeNewLine = true;
 
     @BeforeClass