diff --git a/jetty-start/src/main/java/org/eclipse/jetty/start/Module.java b/jetty-start/src/main/java/org/eclipse/jetty/start/Module.java
index 0425e6314e9b..48802ef4cba0 100644
--- a/jetty-start/src/main/java/org/eclipse/jetty/start/Module.java
+++ b/jetty-start/src/main/java/org/eclipse/jetty/start/Module.java
@@ -417,14 +417,14 @@ public void process(BaseHome basehome) throws FileNotFoundException, IOException
                             case "DEFAULTS": // old name introduced in 9.2.x
                             case "INI": // new name for 9.3+
                             {
-                                // All default properties are to be treated as `<k>?=<v>` by the configuration system
-                                // even if they are present as `<k>=<v>`
+                                // If a property is specified as `<k>=<v>` it is to be treated as `<k>?=<v>`.
+                                // All other property usages are left as-is (eg: `<k>+=<v>`)
                                 int idx = line.indexOf('=');
                                 if (idx > 0)
                                 {
                                     String key = line.substring(0, idx);
                                     String value = line.substring(idx + 1);
-                                    if (key.endsWith("?"))
+                                    if (key.endsWith("?") || key.endsWith("+"))
                                     {
                                         // already the correct way
                                         _defaultConfig.add(line);
diff --git a/tests/test-distribution/src/test/java/org/eclipse/jetty/tests/distribution/DemoModulesTests.java b/tests/test-distribution/src/test/java/org/eclipse/jetty/tests/distribution/DemoModulesTests.java
index 55f35976e5d6..09c977c42bbc 100644
--- a/tests/test-distribution/src/test/java/org/eclipse/jetty/tests/distribution/DemoModulesTests.java
+++ b/tests/test-distribution/src/test/java/org/eclipse/jetty/tests/distribution/DemoModulesTests.java
@@ -15,8 +15,8 @@
 
 import java.net.URI;
 import java.nio.file.Path;
+import java.util.NoSuchElementException;
 import java.util.concurrent.TimeUnit;
-import java.util.function.Supplier;
 
 import org.eclipse.jetty.client.api.ContentResponse;
 import org.eclipse.jetty.client.util.FormRequestContent;
@@ -27,6 +27,7 @@
 
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.greaterThan;
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.not;
 import static org.junit.jupiter.api.Assertions.assertEquals;
@@ -34,6 +35,49 @@
 
 public class DemoModulesTests extends AbstractJettyHomeTest
 {
+    @Test
+    public void testDemoAddServerClasses() throws Exception
+    {
+        Path jettyBase = newTestJettyBaseDirectory();
+        String jettyVersion = System.getProperty("jettyVersion");
+        JettyHomeTester distribution = JettyHomeTester.Builder.newInstance()
+            .jettyVersion(jettyVersion)
+            .jettyBase(jettyBase)
+            .mavenLocalRepository(System.getProperty("mavenRepoPath"))
+            .build();
+
+        int httpPort = distribution.freePort();
+        int httpsPort = distribution.freePort();
+        assertThat("httpPort != httpsPort", httpPort, is(not(httpsPort)));
+
+        String[] argsConfig = {
+            "--add-modules=demo"
+        };
+
+        try (JettyHomeTester.Run runConfig = distribution.start(argsConfig))
+        {
+            assertTrue(runConfig.awaitFor(5, TimeUnit.SECONDS));
+            assertEquals(0, runConfig.getExitValue());
+
+            try (JettyHomeTester.Run runListConfig = distribution.start("--list-config"))
+            {
+                assertTrue(runListConfig.awaitFor(5, TimeUnit.SECONDS));
+                assertEquals(0, runListConfig.getExitValue());
+                // Example of what we expect
+                // jetty.webapp.addServerClasses = org.eclipse.jetty.logging.,${jetty.home.uri}/lib/logging/,org.slf4j.,${jetty.base.uri}/lib/bouncycastle/
+                String addServerKey = " jetty.webapp.addServerClasses = ";
+                String addServerClasses = runListConfig.getLogs().stream()
+                    .filter(s -> s.startsWith(addServerKey))
+                    .findFirst()
+                    .orElseThrow(() ->
+                        new NoSuchElementException("Unable to find [" + addServerKey + "]"));
+                assertThat("'jetty.webapp.addServerClasses' entry count",
+                    addServerClasses.split(",").length,
+                    greaterThan(1));
+            }
+        }
+    }
+
     @Test
     public void testJspDump() throws Exception
     {