diff --git a/composer.json b/composer.json
index 646fd94203..9f16348bd6 100644
--- a/composer.json
+++ b/composer.json
@@ -52,7 +52,7 @@
         "post-autoload-dump": "Drupal\\Core\\Composer\\Composer::ensureHtaccess",
         "post-package-install": "Drupal\\Core\\Composer\\Composer::vendorTestCodeCleanup",
         "post-package-update": "Drupal\\Core\\Composer\\Composer::vendorTestCodeCleanup",
-        "post-install-cmd": "Drupal\\Core\\Composer\\Composer::upgradePHPUnit",
+        "drupal-phpunit-upgrade-check": "Drupal\\Core\\Composer\\Composer::upgradePHPUnit",
         "drupal-phpunit-upgrade": "@composer update phpunit/phpunit --with-dependencies --no-progress",
         "phpcs": "phpcs --standard=core/phpcs.xml.dist --runtime-set installed_paths $($COMPOSER_BINARY config vendor-dir)/drupal/coder/coder_sniffer --",
         "phpcbf": "phpcbf --standard=core/phpcs.xml.dist --runtime-set installed_paths $($COMPOSER_BINARY config vendor-dir)/drupal/coder/coder_sniffer --"
diff --git a/core/scripts/run-tests.sh b/core/scripts/run-tests.sh
index ae33bb5410..a97c25d514 100644
--- a/core/scripts/run-tests.sh
+++ b/core/scripts/run-tests.sh
@@ -18,6 +18,7 @@
 use Drupal\simpletest\TestBase;
 use Drupal\simpletest\TestDiscovery;
 use PHPUnit\Framework\TestCase;
+use PHPUnit\Runner\Version;
 use Symfony\Component\HttpFoundation\Request;
 
 $autoloader = require_once __DIR__ . '/../../autoload.php';
@@ -141,6 +142,18 @@
   exit(SIMPLETEST_SCRIPT_EXIT_SUCCESS);
 }
 
+// Ensure we have the correct PHPUnit version for the version of PHP.
+if (class_exists('\PHPUnit_Runner_Version')) {
+  $phpunit_version = \PHPUnit_Runner_Version::id();
+}
+else {
+  $phpunit_version = Version::id();
+}
+if (version_compare(PHP_MAJOR_VERSION . '.' . PHP_MINOR_VERSION, '7.2') >= 0 && version_compare($phpunit_version, '6.1') < 0) {
+  echo "\nrun-tests.sh requires the PHPUnit testing framework version 6 or greater when running on PHP 7.2 or greater. Please use 'composer run-script drupal-phpunit-upgrade' to ensure that it is present.\n\n";
+  exit(SIMPLETEST_SCRIPT_EXIT_FAILURE);
+}
+
 $test_list = simpletest_script_get_test_list();
 
 // Try to allocate unlimited time to run the tests.
@@ -520,6 +533,9 @@ function simpletest_script_init() {
   }
 
   chdir(realpath(__DIR__ . '/../..'));
+  if (!$args['execute-test']) {
+    shell_exec('composer run-script drupal-phpunit-upgrade-check');
+  }
 }
 
 /**
diff --git a/core/tests/bootstrap.php b/core/tests/bootstrap.php
index 50fef61ee6..d376a06de3 100644
--- a/core/tests/bootstrap.php
+++ b/core/tests/bootstrap.php
@@ -168,9 +168,20 @@ function drupal_phpunit_populate_class_loader() {
 // not turn runtime assertions on if they weren't on already.
 Handle::register();
 
+// Ensure we have the correct PHPUnit version for the version of PHP.
+if (class_exists('\PHPUnit_Runner_Version')) {
+  $phpunit_version = \PHPUnit_Runner_Version::id();
+}
+else {
+  $phpunit_version = Version::id();
+}
+if (version_compare(PHP_MAJOR_VERSION . '.' . PHP_MINOR_VERSION, '7.2') >= 0 && version_compare($phpunit_version, '6.1') < 0) {
+  echo "\nTesting Drupal requires the PHPUnit testing framework version 6 or greater when running on PHP 7.2 or greater. Please use 'composer run-script drupal-phpunit-upgrade' to ensure that it is present.\n\n";
+  exit(1);
+}
 // PHPUnit 4 to PHPUnit 6 bridge. Tests written for PHPUnit 4 need to work on
 // PHPUnit 6 with a minimum of fuss.
-if (class_exists('PHPUnit\Runner\Version') && version_compare(Version::id(), '6.1', '>=')) {
+if (version_compare($phpunit_version, '6.1', '>=')) {
   class_alias('\PHPUnit\Framework\AssertionFailedError', '\PHPUnit_Framework_AssertionFailedError');
   class_alias('\PHPUnit\Framework\Constraint\Count', '\PHPUnit_Framework_Constraint_Count');
   class_alias('\PHPUnit\Framework\Error\Error', '\PHPUnit_Framework_Error');