diff --git a/plugin/src/main/java/org/elasticsearch/xpack/extensions/InstallXPackExtensionCommand.java b/plugin/src/main/java/org/elasticsearch/xpack/extensions/InstallXPackExtensionCommand.java
index b3da5bc308a..0582052a671 100644
--- a/plugin/src/main/java/org/elasticsearch/xpack/extensions/InstallXPackExtensionCommand.java
+++ b/plugin/src/main/java/org/elasticsearch/xpack/extensions/InstallXPackExtensionCommand.java
@@ -28,10 +28,12 @@ import java.nio.file.Path;
 import java.nio.file.StandardCopyOption;
 
 import java.util.Arrays;
+import java.util.HashSet;
 import java.util.List;
 import java.util.ArrayList;
 import java.util.Comparator;
 import java.util.Collections;
+import java.util.Set;
 import java.util.zip.ZipEntry;
 import java.util.zip.ZipInputStream;
 
@@ -168,8 +170,7 @@ final class InstallXPackExtensionCommand extends EnvironmentAwareCommand {
     private void jarHellCheck(Path candidate) throws Exception {
         // create list of current jars in classpath
         // including the x-pack jars (see $ES_CLASSPATH in bin/extension script)
-        final List<URL> jars = new ArrayList<>();
-        jars.addAll(Arrays.asList(JarHell.parseClassPath()));
+        final Set<URL> jars = new HashSet<>(JarHell.parseClassPath());
 
         // add extension jars to the list
         Path extensionJars[] = FileSystemUtils.files(candidate, "*.jar");
@@ -180,7 +181,7 @@ final class InstallXPackExtensionCommand extends EnvironmentAwareCommand {
         // TODO: verify the classname exists in one of the jars!
 
         // check combined (current classpath + new jars to-be-added)
-        JarHell.checkJarHell(jars.toArray(new URL[jars.size()]));
+        JarHell.checkJarHell(jars);
     }
 
     /**
diff --git a/plugin/src/main/java/org/elasticsearch/xpack/extensions/XPackExtensionsService.java b/plugin/src/main/java/org/elasticsearch/xpack/extensions/XPackExtensionsService.java
index 69d1757e654..361d20bbd3e 100644
--- a/plugin/src/main/java/org/elasticsearch/xpack/extensions/XPackExtensionsService.java
+++ b/plugin/src/main/java/org/elasticsearch/xpack/extensions/XPackExtensionsService.java
@@ -5,14 +5,6 @@
  */
 package org.elasticsearch.xpack.extensions;
 
-import org.apache.logging.log4j.Logger;
-import org.elasticsearch.ElasticsearchException;
-import org.elasticsearch.bootstrap.JarHell;
-import org.elasticsearch.common.collect.Tuple;
-import org.elasticsearch.common.io.FileSystemUtils;
-import org.elasticsearch.common.logging.Loggers;
-import org.elasticsearch.common.settings.Settings;
-
 import java.io.IOException;
 import java.net.URL;
 import java.net.URLClassLoader;
@@ -23,9 +15,19 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.LinkedHashSet;
 import java.util.List;
+import java.util.Set;
 import java.util.stream.Collectors;
 
+import org.apache.logging.log4j.Logger;
+import org.elasticsearch.ElasticsearchException;
+import org.elasticsearch.bootstrap.JarHell;
+import org.elasticsearch.common.collect.Tuple;
+import org.elasticsearch.common.io.FileSystemUtils;
+import org.elasticsearch.common.logging.Loggers;
+import org.elasticsearch.common.settings.Settings;
+
 import static org.elasticsearch.common.io.FileSystemUtils.isAccessibleDirectory;
 
 public class XPackExtensionsService {
@@ -132,9 +134,9 @@ public class XPackExtensionsService {
             // jar-hell check the bundle against the parent classloader and the x-pack classloader
             // pluginmanager does it, but we do it again, in case lusers mess with jar files manually
             try {
-                final List<URL> jars = new ArrayList<>();
+                final Set<URL> jars = new LinkedHashSet<>();
                 // add the parent jars to the list
-                jars.addAll(Arrays.asList(JarHell.parseClassPath()));
+                jars.addAll(JarHell.parseClassPath());
 
                 // add the x-pack jars to the list
                 ClassLoader xpackLoader = getClass().getClassLoader();
@@ -145,7 +147,7 @@ public class XPackExtensionsService {
 
                 jars.addAll(bundle.urls);
 
-                JarHell.checkJarHell(jars.toArray(new URL[0]));
+                JarHell.checkJarHell(jars);
             } catch (Exception e) {
                 throw new IllegalStateException("failed to load bundle " + bundle.urls + " due to jar hell", e);
             }