diff --git a/src/Peachpied.PhpUnit.TestAdapter/EnvironmentHelper.cs b/src/Peachpied.PhpUnit.TestAdapter/EnvironmentHelper.cs
index 4608004..84cb314 100644
--- a/src/Peachpied.PhpUnit.TestAdapter/EnvironmentHelper.cs
+++ b/src/Peachpied.PhpUnit.TestAdapter/EnvironmentHelper.cs
@@ -34,5 +34,20 @@ namespace Peachpied.PhpUnit.TestAdapter
                 return assemblyDir;
             }
         }
+
+        /// <summary>
+        /// Generate a file name in the given directory with the given prefix which
+        /// does not exists in it yet.
+        /// </summary>
+        public static string GetNonexistingFilePath(string dir, string prefix = "")
+        {
+            string filePath;
+            do
+            {
+                filePath = Path.Combine(dir, prefix + Path.GetRandomFileName());
+            } while (File.Exists(filePath));
+
+            return filePath;
+        }
     }
 }
diff --git a/src/Peachpied.PhpUnit.TestAdapter/PhpUnitHelper.cs b/src/Peachpied.PhpUnit.TestAdapter/PhpUnitHelper.cs
index c2f9eb1..4a219fd 100644
--- a/src/Peachpied.PhpUnit.TestAdapter/PhpUnitHelper.cs
+++ b/src/Peachpied.PhpUnit.TestAdapter/PhpUnitHelper.cs
@@ -4,6 +4,7 @@ using PHPUnit.Framework;
 using PHPUnit.TextUI;
 using System;
 using System.Collections.Generic;
+using System.IO;
 using System.Reflection;
 using System.Text;
 
@@ -14,6 +15,11 @@ namespace Peachpied.PhpUnit.TestAdapter
     /// </summary>
     internal static class PhpUnitHelper
     {
+        /// <summary>
+        /// Current PHPUnit version.
+        /// </summary>
+        public static Version Version { get; } = typeof(TestCase).Assembly.GetName().Version;
+
         private const string PharName = "phpunit.phar";
 
         static PhpUnitHelper()
@@ -22,10 +28,30 @@ namespace Peachpied.PhpUnit.TestAdapter
             Context.AddScriptReference(typeof(TestCase).Assembly);
         }
 
+        /// <summary>
+        /// Find a PHPUnit configuration file in the given directory, return <c>null</c> if not present.
+        /// </summary>
+        public static string TryFindConfigFile(string dir)
+        {
+            string primaryConfig = Path.Combine(dir, "phpunit.xml");
+            if (File.Exists(primaryConfig))
+            {
+                return primaryConfig;
+            }
+
+            string secondaryConfig = Path.Combine(dir, "phpunit.xml.dist");
+            if (File.Exists(secondaryConfig))
+            {
+                return secondaryConfig;
+            }
+
+            return null;
+        }
+
         /// <summary>
         /// Run PHPUnit on the given assembly and command line arguments.
         /// </summary>
-        public static void Launch(string cwd, string testedAssembly, string[] args, Action<Context> initCalblack = null, Action<Context> finishCallback = null)
+        public static void Launch(string cwd, string testedAssembly, string[] args, Action<Context> initCallback = null, Action<Context> finishCallback = null)
         {
             // Load assembly with tests (if not loaded yet)
             Context.AddScriptReference(Assembly.LoadFrom(testedAssembly));
@@ -39,7 +65,7 @@ namespace Peachpied.PhpUnit.TestAdapter
                 ctx.Server[CommonPhpArrayKeys.SCRIPT_NAME] = "__DUMMY_INVALID_FILE";
 
                 // Perform any custom operations on the context
-                initCalblack?.Invoke(ctx);
+                initCallback?.Invoke(ctx);
 
                 // Run the PHAR entry point so that all the classes are included
                 var pharLoader = Context.TryGetDeclaredScript(PharName);
diff --git a/src/Peachpied.PhpUnit.TestAdapter/PhpUnitTestExecutor.cs b/src/Peachpied.PhpUnit.TestAdapter/PhpUnitTestExecutor.cs
index a506774..1e825f3 100644
--- a/src/Peachpied.PhpUnit.TestAdapter/PhpUnitTestExecutor.cs
+++ b/src/Peachpied.PhpUnit.TestAdapter/PhpUnitTestExecutor.cs
@@ -1,11 +1,15 @@
 using Microsoft.VisualStudio.TestPlatform.ObjectModel;
 using Microsoft.VisualStudio.TestPlatform.ObjectModel.Adapter;
 using Microsoft.VisualStudio.TestPlatform.ObjectModel.Logging;
+using Pchp.Core;
 using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Text;
 using System.Text.RegularExpressions;
+using System.Xml;
+using System.Xml.Linq;
 
 namespace Peachpied.PhpUnit.TestAdapter
 {
@@ -44,8 +48,7 @@ namespace Peachpied.PhpUnit.TestAdapter
         {
             try
             {
-                // Inject our custom extension to report the test results
-                var args = new[] { "--extensions", TestReporterExtension.PhpName };
+                var args = Array.Empty<string>();
 
                 // Optionally filter the test cases by their names
                 if (testCases != null)
@@ -62,7 +65,8 @@ namespace Peachpied.PhpUnit.TestAdapter
 
                 string projectDir = EnvironmentHelper.TryFindProjectDirectory(Path.GetDirectoryName(source));
 
-                PhpUnitHelper.Launch(projectDir, source, args,
+                // Inject our custom extension to report the test results
+                RunPhpUnitWithExtension(projectDir, source, args,
                     ctx =>
                     {
                         // Enable Peachpie to create an instance of our custom extension
@@ -79,6 +83,52 @@ namespace Peachpied.PhpUnit.TestAdapter
             }
         }
 
+        private void RunPhpUnitWithExtension(string projectDir, string source, string[] args, Action<Context> initCallback)
+        {
+            if (PhpUnitHelper.Version >= new Version(9, 1))
+            {
+                // The --extensions CLI argument is available from PHPUnit 9.1 (although it's documented only from 9.3)
+                args = new[] { "--extensions", TestReporterExtension.PhpName }.Concat(args).ToArray();
+                PhpUnitHelper.Launch(projectDir, source, args, initCallback);
+            }
+            else
+            {
+                // Older PHPUnit versions can receive extensions only in the configuration file,
+                // so we need to create a modified version of the existing one and pass it to PHPUnit.
+                // (or create one from scratch it if it doesn't exist at all)
+
+                // Create PHPUnit configuration with the extension added
+                string origConfigFile = PhpUnitHelper.TryFindConfigFile(projectDir);
+                var configXml = (origConfigFile != null) ? XElement.Load(origConfigFile) : new XElement("phpunit");
+                var extensionsEl = configXml.GetOrCreateElement("extensions");
+                extensionsEl.Add(new XElement("extension", new XAttribute("class", TestReporterExtension.PhpName)));
+
+                // Store the configuration in a temporary file to pass it to PHPUnit
+                string tempConfigFile = null;
+                try
+                {
+                    // The configuration file must be in the same folder as the project in order to work (to load PHP classes properly etc.)
+                    tempConfigFile = EnvironmentHelper.GetNonexistingFilePath(projectDir, "phpunit.xml.");
+
+                    // Save the config file without the BOM
+                    using (var xmlWriter = new XmlTextWriter(tempConfigFile, new UTF8Encoding(encoderShouldEmitUTF8Identifier: false)))
+                    {
+                        configXml.Save(xmlWriter);
+                    }
+
+                    args = new[] { "--configuration", tempConfigFile }.Concat(args).ToArray();
+                    PhpUnitHelper.Launch(projectDir, source, args, initCallback);
+                }
+                finally
+                {
+                    if (File.Exists(tempConfigFile))
+                    {
+                        File.Delete(tempConfigFile);
+                    }
+                }
+            }
+        }
+
         /// <summary>
         /// Cancel test execution, currently ignored.
         /// </summary>
diff --git a/src/Peachpied.PhpUnit.TestAdapter/XElementExtensions.cs b/src/Peachpied.PhpUnit.TestAdapter/XElementExtensions.cs
new file mode 100644
index 0000000..735f9c9
--- /dev/null
+++ b/src/Peachpied.PhpUnit.TestAdapter/XElementExtensions.cs
@@ -0,0 +1,28 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Xml.Linq;
+
+namespace Peachpied.PhpUnit.TestAdapter
+{
+    /// <summary>
+    /// LINQ to XML utility methods.
+    /// </summary>
+    internal static class XElementExtensions
+    {
+        /// <summary>
+        /// Retrieve the child element of the given name if it exists, or add an empty new one if it doesn't exist.
+        /// </summary>
+        public static XElement GetOrCreateElement(this XElement parent, XName elementName)
+        {
+            var element = parent.Element(elementName);
+            if (element == null)
+            {
+                element = new XElement(elementName);
+                parent.Add(element);
+            }
+
+            return element;
+        }
+    }
+}