diff --git a/ant/org.eclipse.ant.launching/src/org/eclipse/ant/internal/launching/launchConfigurations/AntLaunchDelegate.java b/ant/org.eclipse.ant.launching/src/org/eclipse/ant/internal/launching/launchConfigurations/AntLaunchDelegate.java
index 01db6f9..c09cea6 100644
--- a/ant/org.eclipse.ant.launching/src/org/eclipse/ant/internal/launching/launchConfigurations/AntLaunchDelegate.java
+++ b/ant/org.eclipse.ant.launching/src/org/eclipse/ant/internal/launching/launchConfigurations/AntLaunchDelegate.java
@@ -141,6 +141,14 @@
 				}
 			}
 		}
+		if (vmver == null) {
+			IVMInstall vm = JavaRuntime.getDefaultVMInstall();
+			if (vm instanceof AbstractVMInstall) {
+				AbstractVMInstall install = (AbstractVMInstall) vm;
+				vmver = install.getJavaVersion();
+			}
+
+		}
 		if (monitor.isCanceled()) {
 			return;
 		}
@@ -450,7 +458,8 @@
 			commandLine.append(antHome);
 			commandLine.append('\"');
 		}
-		if (vmver != null && JavaCore.compareJavaVersions(vmver, JavaCore.VERSION_17) >= 0) {
+		if (vmver != null && JavaCore.compareJavaVersions(vmver, JavaCore.VERSION_17) >= 0
+				&& commandLine.indexOf("-Djava.security.manager=allow") == -1) { //$NON-NLS-1$
 			commandLine.append(" \"-Djava.security.manager=allow\""); //$NON-NLS-1$
 		}