diff --git a/ant/org.eclipse.ant.core/src_ant/org/eclipse/ant/internal/core/ant/InternalAntRunner.java b/ant/org.eclipse.ant.core/src_ant/org/eclipse/ant/internal/core/ant/InternalAntRunner.java
index 78a78d5f512..9f24bc20c46 100644
--- a/ant/org.eclipse.ant.core/src_ant/org/eclipse/ant/internal/core/ant/InternalAntRunner.java
+++ b/ant/org.eclipse.ant.core/src_ant/org/eclipse/ant/internal/core/ant/InternalAntRunner.java
@@ -52,6 +52,7 @@
 import org.apache.tools.ant.Target;
 import org.apache.tools.ant.TaskAdapter;
 import org.apache.tools.ant.XmlLogger;
+import org.apache.tools.ant.util.JavaEnvUtils;
 import org.eclipse.ant.core.AntCorePlugin;
 import org.eclipse.ant.core.AntCorePreferences;
 import org.eclipse.ant.core.AntSecurityException;
@@ -82,6 +83,17 @@
 @SuppressWarnings("removal") // SecurityManager
 public class InternalAntRunner {
 
+	private static final boolean IS_SECURITY_MANAGER_SUPPORTED = isSecurityManagerAllowed();
+
+	private static boolean isSecurityManagerAllowed() {
+		String sm = System.getProperty("java.security.manager"); //$NON-NLS-1$
+		if (sm == null) { // default is 'disallow' since 18 and was 'allow' before
+			return !JavaEnvUtils.isAtLeastJavaVersion("18"); //$NON-NLS-1$
+		}
+		// Value is either 'disallow' or 'allow' or specifies the SecurityManager class to set
+		return !"disallow".equals(sm); //$NON-NLS-1$
+	}
+
 	private IProgressMonitor monitor;
 	private ArrayList<String> buildListeners;
 	private String buildFileLocation;
@@ -695,12 +707,11 @@ private void run(List<String> argList) {
 			if (extraArguments != null) {
 				printArguments(getCurrentProject());
 			}
-			try {
+			if (IS_SECURITY_MANAGER_SUPPORTED) {
+				// TODO: call SecurityManagerUtil.isSecurityManagerAllowed() once it's more fine-grained,
+				// i.e. once https://github.com/apache/ant/pull/216 is available.
 				System.setSecurityManager(new AntSecurityManager(originalSM, Thread.currentThread()));
 			}
-			catch (UnsupportedOperationException ex) {
-				AntCorePlugin.getPlugin().getLog().log(new Status(IStatus.ERROR, AntCorePlugin.PI_ANTCORE, 0, InternalAntMessages.InternalAntRunner_SecurityManagerError, ex));
-			}
 			if (targets == null) {
 				targets = new Vector<>(1);
 			}
@@ -1432,9 +1443,7 @@ protected void loadPropertyFiles() {
 		}
 		try {
 			List<Properties> allProperties = AntCoreUtil.loadPropertyFiles(propertyFiles, currentProject.getUserProperty("basedir"), getBuildFileLocation()); //$NON-NLS-1$
-			Iterator<Properties> iter = allProperties.iterator();
-			while (iter.hasNext()) {
-				Properties props = iter.next();
+			for (Properties props : allProperties) {
 				Enumeration<?> propertyNames = props.propertyNames();
 				while (propertyNames.hasMoreElements()) {
 					String name = (String) propertyNames.nextElement();
diff --git a/ant/org.eclipse.ant.tests.core/test plugin/org/eclipse/ant/tests/core/testplugin/AntTestChecker.java b/ant/org.eclipse.ant.tests.core/test plugin/org/eclipse/ant/tests/core/testplugin/AntTestChecker.java
index 1ede0d34e1c..beff191668a 100644
--- a/ant/org.eclipse.ant.tests.core/test plugin/org/eclipse/ant/tests/core/testplugin/AntTestChecker.java	
+++ b/ant/org.eclipse.ant.tests.core/test plugin/org/eclipse/ant/tests/core/testplugin/AntTestChecker.java	
@@ -14,6 +14,7 @@
 package org.eclipse.ant.tests.core.testplugin;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.Hashtable;
 import java.util.List;
 
@@ -219,7 +220,7 @@ public String getUserProperty(String name) {
 	}
 
 	public List<String> getMessages() {
-		return messages;
+		return Collections.unmodifiableList(messages);
 	}
 
 	public List<String> getListeners() {