diff --git a/src/main/java/org/jvnet/hudson/test/RealJenkinsRule.java b/src/main/java/org/jvnet/hudson/test/RealJenkinsRule.java
index 5e0fa5c87..9c7fd88c5 100644
--- a/src/main/java/org/jvnet/hudson/test/RealJenkinsRule.java
+++ b/src/main/java/org/jvnet/hudson/test/RealJenkinsRule.java
@@ -1734,8 +1734,17 @@ public RealJenkinsRule done() {
         }
 
         void writeTo(File jpi, String defaultJenkinsVersion) throws IOException, URISyntaxException {
-            ByteArrayOutputStream baos = new ByteArrayOutputStream();
-            try (ZipOutputStream zos = new ZipOutputStream(baos)) {
+            var mani = new Manifest();
+            var attr = mani.getMainAttributes();
+            attr.put(Attributes.Name.MANIFEST_VERSION, "1.0");
+            attr.putValue("Short-Name", shortName);
+            attr.putValue("Plugin-Version", version);
+            attr.putValue("Jenkins-Version", defaultJenkinsVersion);
+            for (var entry : headers.entrySet()) {
+                attr.putValue(entry.getKey(), entry.getValue());
+            }
+            var jar = new ByteArrayOutputStream();
+            try (var jos = new JarOutputStream(jar, mani)) {
                 String pkgSlash = pkg.replace('.', '/');
                 URL mainU = RealJenkinsRule.class.getClassLoader().getResource(pkgSlash);
                 if (mainU == null) {
@@ -1747,22 +1756,13 @@ void writeTo(File jpi, String defaultJenkinsVersion) throws IOException, URISynt
                 }
                 Path metaInf = Path.of(URI.create(mainU.toString().replaceFirst("\\Q" + pkgSlash + "\\E/?$", "META-INF")));
                 if (Files.isDirectory(metaInf)) {
-                    zip(zos, metaInf, "META-INF/", pkg);
+                    zip(jos, metaInf, "META-INF/", pkg);
                 }
-                zip(zos, main, pkgSlash + "/", null);
-            }
-            Manifest mani = new Manifest();
-            Attributes attr = mani.getMainAttributes();
-            attr.put(Attributes.Name.MANIFEST_VERSION, "1.0");
-            attr.putValue("Short-Name", shortName);
-            attr.putValue("Plugin-Version", version);
-            attr.putValue("Jenkins-Version", defaultJenkinsVersion);
-            for (Map.Entry<String, String> entry : headers.entrySet()) {
-                attr.putValue(entry.getKey(), entry.getValue());
+                zip(jos, main, pkgSlash + "/", null);
             }
-            try (OutputStream os = new FileOutputStream(jpi); JarOutputStream jos = new JarOutputStream(os, mani)) {
+            try (var os = new FileOutputStream(jpi); var jos = new JarOutputStream(os, mani)) {
                 jos.putNextEntry(new JarEntry("WEB-INF/lib/" + shortName + ".jar"));
-                jos.write(baos.toByteArray());
+                jos.write(jar.toByteArray());
             }
             LOGGER.info(() -> "Generated " + jpi);
         }
diff --git a/src/test/java/org/jvnet/hudson/test/RealJenkinsRuleSyntheticPluginTest.java b/src/test/java/org/jvnet/hudson/test/RealJenkinsRuleSyntheticPluginTest.java
index cf5582af6..dc4a2b203 100644
--- a/src/test/java/org/jvnet/hudson/test/RealJenkinsRuleSyntheticPluginTest.java
+++ b/src/test/java/org/jvnet/hudson/test/RealJenkinsRuleSyntheticPluginTest.java
@@ -24,11 +24,15 @@
 
 package org.jvnet.hudson.test;
 
+import java.util.logging.Level;
 import jenkins.model.Jenkins;
+import jenkins.security.ClassFilterImpl;
 import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.is;
 import org.junit.Rule;
 import org.junit.Test;
+import org.jvnet.hudson.test.sample.plugin.CustomJobProperty;
 import org.jvnet.hudson.test.sample.plugin.Stuff;
 
 public final class RealJenkinsRuleSyntheticPluginTest {
@@ -45,4 +49,13 @@ private static void _smokes(JenkinsRule r) throws Throwable {
             is(Jenkins.get().getLegacyInstanceId()));
     }
 
+    @Test public void classFilter() throws Throwable {
+        rr.addSyntheticPlugin(CustomJobProperty.class.getPackage()).done().withLogger(ClassFilterImpl.class, Level.FINE);
+        rr.then(r -> {
+            var p = r.createFreeStyleProject();
+            p.addProperty(new CustomJobProperty("expected in XML"));
+            assertThat(p.getConfigFile().asString(), containsString("expected in XML"));
+        });
+    }
+
 }
diff --git a/src/test/java/org/jvnet/hudson/test/sample/plugin/CustomJobProperty.java b/src/test/java/org/jvnet/hudson/test/sample/plugin/CustomJobProperty.java
new file mode 100644
index 000000000..d5ca47f14
--- /dev/null
+++ b/src/test/java/org/jvnet/hudson/test/sample/plugin/CustomJobProperty.java
@@ -0,0 +1,42 @@
+/*
+ * The MIT License
+ *
+ * Copyright 2025 CloudBees, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package org.jvnet.hudson.test.sample.plugin;
+
+import hudson.model.Job;
+import hudson.model.JobProperty;
+
+/**
+ * Sample describable.
+ * @see RealJenkinsRuleSyntheticPluginTest
+ */
+public final class CustomJobProperty extends JobProperty<Job<?, ?>> {
+
+    private final String value;
+
+    public CustomJobProperty(String value) {
+        this.value = value;
+    }
+
+}