diff --git a/core/modules/simpletest/simpletest.install b/core/modules/simpletest/simpletest.install
index c1422e6e702e63725946711c3375e512caa3c3f4..0e3cd00d5fc09d904437471ddd2254ea8ff11837 100644
--- a/core/modules/simpletest/simpletest.install
+++ b/core/modules/simpletest/simpletest.install
@@ -18,9 +18,19 @@
 function simpletest_requirements($phase) {
   $requirements = array();
 
+  $has_phpunit = class_exists('\PHPUnit_Framework_TestCase');
   $has_curl = function_exists('curl_init');
   $open_basedir = ini_get('open_basedir');
 
+  $requirements['phpunit'] = array(
+    'title' => t('PHPUnit dependency'),
+    'value' => $has_phpunit ? t('Found') : t('Not found'),
+  );
+  if (!$has_phpunit) {
+    $requirements['phpunit']['severity'] = REQUIREMENT_ERROR;
+    $requirements['phpunit']['description'] = t("The testing framework requires the PHPUnit package. Please run 'composer install --dev' to ensure it is present.");
+  }
+
   $requirements['curl'] = array(
     'title' => t('cURL'),
     'value' => $has_curl ? t('Enabled') : t('Not found'),
diff --git a/core/scripts/run-tests.sh b/core/scripts/run-tests.sh
index a981c25aa62636b391af8c0c15a5591ef06e079b..cd00d7431e7c668a3e9412ec14f3a408dc40e6d8 100755
--- a/core/scripts/run-tests.sh
+++ b/core/scripts/run-tests.sh
@@ -34,6 +34,11 @@
 const SIMPLETEST_SCRIPT_EXIT_FAILURE = 1;
 const SIMPLETEST_SCRIPT_EXIT_EXCEPTION = 2;
 
+if (!class_exists('\PHPUnit_Framework_TestCase')) {
+  echo "\nrun-tests.sh requires the PHPUnit testing framework. Please use 'composer install --dev' to ensure that it is present.\n\n";
+  exit(SIMPLETEST_SCRIPT_EXIT_FAILURE);
+}
+
 // Set defaults and get overrides.
 list($args, $count) = simpletest_script_parse_args();