diff --git a/core/src/main/java/io/apigee/trireme/core/Sandbox.java b/core/src/main/java/io/apigee/trireme/core/Sandbox.java
index a84efa88..7cf8061f 100644
--- a/core/src/main/java/io/apigee/trireme/core/Sandbox.java
+++ b/core/src/main/java/io/apigee/trireme/core/Sandbox.java
@@ -27,6 +27,8 @@
 
 import java.io.InputStream;
 import java.io.OutputStream;
+import java.net.URL;
+import java.net.URLClassLoader;
 import java.util.AbstractMap;
 import java.util.ArrayList;
 import java.util.List;
@@ -55,7 +57,7 @@ public class Sandbox
     private boolean         hideOsDetails;
     private ClassShutter    extraClassShutter;
     private boolean         allowJarLoading = true;
-    private ClassLoader     classLoader = null;
+    private ClassLoaderSupplier classLoaderSupplier = null;
 
     /**
      * Create a new sandbox that will not affect anything in any way.
@@ -85,7 +87,7 @@ public Sandbox(Sandbox parent)
             this.hideOsDetails = parent.hideOsDetails;
             this.extraClassShutter = parent.extraClassShutter;
             this.allowJarLoading = parent.allowJarLoading;
-            this.classLoader = parent.classLoader;
+            this.classLoaderSupplier = parent.classLoaderSupplier;
             if (parent.mounts != null) {
                 this.mounts = new ArrayList<Map.Entry<String, String>>(parent.mounts);
             }
@@ -279,15 +281,36 @@ public boolean isAllowJarLoading() {
     }
 
     /**
-     * Allows specifying the ClassLoader that will be used by the "trireme-support" module's
-     * "loadJars" method to load JAR files into the currently-running script.
+     * A Supplier that returns an instance of a ClassLoader to be used
+     * for loading Java classes into the currently-running script.
+     * <p/>
+     * The Supplier should return a new instance for every invocation of this method
+     * if it is desired that classes loaded by any one invocation of the
+     * "trireme-support" module's "loadJars" method are isolated from classes loaded
+     * from another invocation of the "loadJars" method.
+     * <p/>
+     * The Supplier may return the same instance for every invocation of this method
+     * if such isolation is not desired.
      */
-    public Sandbox setClassLoader(ClassLoader classLoader) {
-        this.classLoader = classLoader;
+    public interface ClassLoaderSupplier {
+        ClassLoader getClassLoader(URL[] urlArray);
+    }
+
+    /**
+     * Allows specifying the Supplier that will return an instance of a ClassLoader
+     * that will be used by the "trireme-support" module's "loadJars" method to load JAR files
+     * into the currently-running script.
+     */
+    public Sandbox setClassLoaderSupplier(ClassLoaderSupplier classLoaderSupplier) {
+        this.classLoaderSupplier = classLoaderSupplier;
         return this;
     }
 
-    public ClassLoader getClassLoader() {
-        return classLoader;
+    /**
+     * Returns the ClassLoaderSupplier if set, null otherwise.
+     */
+    public ClassLoaderSupplier getClassLoaderSupplier() {
+        return classLoaderSupplier;
     }
+
 }
diff --git a/core/src/main/java/io/apigee/trireme/core/modules/TriremeNativeSupport.java b/core/src/main/java/io/apigee/trireme/core/modules/TriremeNativeSupport.java
index 445fff49..f24fdfcc 100644
--- a/core/src/main/java/io/apigee/trireme/core/modules/TriremeNativeSupport.java
+++ b/core/src/main/java/io/apigee/trireme/core/modules/TriremeNativeSupport.java
@@ -99,14 +99,18 @@ public static Object loadJars(Context cx, Scriptable thisObj, Object[] args, Fun
                     throw Utils.makeError(cx, thisObj, "Cannot get URL for JAR file :" + e);
                 }
             }
+            URL[] urlArray = urls.toArray(new URL[urls.size()]);
 
             Sandbox sandbox = self.runtime.getSandbox();
             ClassLoader loader = null;
             if (sandbox != null) { // use custom class loader if specified
-                loader = sandbox.getClassLoader();
+                Sandbox.ClassLoaderSupplier supplier = sandbox.getClassLoaderSupplier();
+                if (supplier != null) {
+                    loader = supplier.getClassLoader(urlArray);
+                }
             }
             if (loader == null) { // fallback
-                loader = new URLClassLoader(urls.toArray(new URL[urls.size()]));
+                loader = new URLClassLoader(urlArray);
             }
 
             // Load the classes in to the module registry for this script only.
diff --git a/node10/node10src/src/test/java/io/apigee/trireme/node10/test/JarLoadingTest.java b/node10/node10src/src/test/java/io/apigee/trireme/node10/test/JarLoadingTest.java
index ad1c067b..c27c1d18 100644
--- a/node10/node10src/src/test/java/io/apigee/trireme/node10/test/JarLoadingTest.java
+++ b/node10/node10src/src/test/java/io/apigee/trireme/node10/test/JarLoadingTest.java
@@ -106,7 +106,7 @@ public void testLoadingDisabled()
     public void testLoadingUsingCustomClassLoader()
             throws NodeException, InterruptedException, ExecutionException {
 
-        ArrayList<URL> urls = new ArrayList<URL>();
+        final ArrayList<URL> urls = new ArrayList<URL>();
         String[] jarNames = {"target/test-classes/testjar.jar", "target/test-classes/depjar.jar"};
         for (String jn : jarNames) {
             File jarFile = new File(jn);
@@ -121,9 +121,11 @@ public void testLoadingUsingCustomClassLoader()
             }
         }
 
-        Sandbox sb = new Sandbox().setClassLoader(
-                new URLClassLoader(urls.toArray(new URL[urls.size()]))
-        );
+        Sandbox sb = new Sandbox().setClassLoaderSupplier(new Sandbox.ClassLoaderSupplier() {
+            public ClassLoader getClassLoader(URL[] urlArray) {
+                return new URLClassLoader(urls.toArray(new URL[urls.size()]));
+            }
+        });
         NodeScript script = env.createScript("jarload.js",
                 new File("target/test-classes/tests/jarload.js"),
                 new String[]{"Foo", "25"});
@@ -139,8 +141,12 @@ public void testLoadingUsingCustomClassLoader()
     public void testLoadingFailsUsingInvalidCustomClassLoader()
             throws NodeException, InterruptedException, ExecutionException {
 
-        URL empty[] = new URL[0];
-        Sandbox sb = new Sandbox().setClassLoader(new URLClassLoader(empty));
+        final URL empty[] = new URL[0];
+        Sandbox sb = new Sandbox().setClassLoaderSupplier(new Sandbox.ClassLoaderSupplier() {
+            public ClassLoader getClassLoader(URL[] urlArray) {
+                return new URLClassLoader(empty);
+            }
+        });
         NodeScript script = env.createScript("jarload.js",
                 new File("target/test-classes/tests/jarload.js"),
                 new String[]{"Foo", "25"});