diff --git a/log4j-1.2-api/src/main/java/org/apache/log4j/jmx/LoggerDynamicMBean.java b/log4j-1.2-api/src/main/java/org/apache/log4j/jmx/LoggerDynamicMBean.java
index 7be0f070f5f..a2a86d78f41 100644
--- a/log4j-1.2-api/src/main/java/org/apache/log4j/jmx/LoggerDynamicMBean.java
+++ b/log4j-1.2-api/src/main/java/org/apache/log4j/jmx/LoggerDynamicMBean.java
@@ -67,6 +67,10 @@ void addAppender(final String appenderClass, final String appenderName) {
         cat.debug("addAppender called with " + appenderClass + ", " + appenderName);
         final Appender appender =
                 (Appender) OptionConverter.instantiateByClassName(appenderClass, org.apache.log4j.Appender.class, null);
+        if (appender == null) {
+            cat.error("Could not instantiate appender class [" + appenderClass + "] for name [" + appenderName + "].");
+            return;
+        }
         appender.setName(appenderName);
         logger.addAppender(appender);
 
diff --git a/log4j-1.2-api/src/test/java/org/apache/log4j/jmx/LoggerDynamicMBeanTest.java b/log4j-1.2-api/src/test/java/org/apache/log4j/jmx/LoggerDynamicMBeanTest.java
new file mode 100644
index 00000000000..735f6959bb6
--- /dev/null
+++ b/log4j-1.2-api/src/test/java/org/apache/log4j/jmx/LoggerDynamicMBeanTest.java
@@ -0,0 +1,63 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to you under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.log4j.jmx;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.Enumeration;
+import org.apache.log4j.Appender;
+import org.apache.log4j.ConsoleAppender;
+import org.apache.log4j.Logger;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Regression for invalid JMX {@code addAppender} class names: instantiation can
+ * return null and must not NPE when calling {@code setName}.
+ */
+class LoggerDynamicMBeanTest {
+
+    @Test
+    void addAppenderDoesNotNpeWhenClassCannotBeInstantiated() {
+        final Logger logger = Logger.getLogger("jmx.LoggerDynamicMBeanTest.invalid");
+        final LoggerDynamicMBean mbean = new LoggerDynamicMBean(logger);
+
+        assertDoesNotThrow(() -> mbean.addAppender("this.class.does.not.exist.MissingAppender", "should-not-attach"));
+        assertFalse(hasAppenderNamed(logger, "should-not-attach"));
+    }
+
+    @Test
+    void addAppenderStillAttachesValidAppender() {
+        final Logger logger = Logger.getLogger("jmx.LoggerDynamicMBeanTest.valid");
+        final LoggerDynamicMBean mbean = new LoggerDynamicMBean(logger);
+
+        mbean.addAppender(ConsoleAppender.class.getName(), "console-jmx");
+        assertTrue(hasAppenderNamed(logger, "console-jmx"));
+    }
+
+    private static boolean hasAppenderNamed(final Logger logger, final String name) {
+        final Enumeration enumeration = logger.getAllAppenders();
+        while (enumeration.hasMoreElements()) {
+            final Appender appender = (Appender) enumeration.nextElement();
+            if (name.equals(appender.getName())) {
+                return true;
+            }
+        }
+        return false;
+    }
+}
diff --git a/src/changelog/.2.x.x/fix_logger_dynamic_mbean_null_appender.xml b/src/changelog/.2.x.x/fix_logger_dynamic_mbean_null_appender.xml
new file mode 100644
index 00000000000..2e8967364c0
--- /dev/null
+++ b/src/changelog/.2.x.x/fix_logger_dynamic_mbean_null_appender.xml
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns="https://logging.apache.org/xml/ns"
+       xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="fixed">
+  <issue id="4185" link="https://github.com/apache/logging-log4j2/pull/4185"/>
+  <description format="asciidoc">Fix NPE in log4j-1.2-api `LoggerDynamicMBean.addAppender` when the appender class cannot be instantiated</description>
+</entry>