diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index 2031483..25f03bc 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -186,17 +186,22 @@ function system_requirements($phase) {
     ];
   }
 
-  // @todo Remove once update support is dropped.
-  if (drupal_valid_test_ua() || getenv('DRUPAL_DEV_SITE_PATH')) {
-    if (version_compare($phpversion, DRUPAL_MINIMUM_UPDATE_PHP) < 0) {
-      $requirements['php']['description'] = t('Your PHP installation is too old. Drupal requires at least PHP %version.', ['%version' => DRUPAL_MINIMUM_UPDATE_PHP]);
+  if (version_compare($phpversion, DRUPAL_MINIMUM_UPDATE_PHP) < 0) {
+    $requirements['php']['description'] = t('Your PHP installation is too old. Drupal requires at least PHP %version.', ['%version' => DRUPAL_MINIMUM_UPDATE_PHP]);
+    $requirements['php']['severity'] = REQUIREMENT_ERROR;
+    return $requirements;
+  }
+  if (version_compare($phpversion, DRUPAL_MINIMUM_PHP) < 0) {
+    // Allow test installations of Drupal on the minimum update PHP.
+    $is_test_site = drupal_valid_test_ua() || getenv('DRUPAL_DEV_SITE_PATH');
+    if ($phase === 'update') {
+      $requirements['php']['description'] = t('Your PHP installation is too old. Drupal requires at least PHP %version.', ['%version' => DRUPAL_MINIMUM_PHP]);
+      $requirements['php']['severity'] = REQUIREMENT_WARNING;
+    }
+    elseif (!$is_test_site) {
+      $requirements['php']['description'] = t('Your PHP installation is too old. Drupal requires at least PHP %version.', ['%version' => DRUPAL_MINIMUM_PHP]);
       $requirements['php']['severity'] = REQUIREMENT_ERROR;
-      return $requirements;
     }
-  }
-  elseif (version_compare($phpversion, DRUPAL_MINIMUM_PHP) < 0) {
-    $requirements['php']['description'] = t('Your PHP installation is too old. Drupal requires at least PHP %version.', ['%version' => DRUPAL_MINIMUM_PHP]);
-    $requirements['php']['severity'] = ($phase === 'update') ? REQUIREMENT_WARNING : REQUIREMENT_ERROR;
     // If PHP is old, it's not safe to continue with the requirements check.
     return $requirements;
   }
diff --git a/core/modules/system/tests/src/Functional/Update/SystemRequirementsTest.php b/core/modules/system/tests/src/Functional/Update/SystemRequirementsTest.php
new file mode 100644
index 0000000..c9ad3b6
--- /dev/null
+++ b/core/modules/system/tests/src/Functional/Update/SystemRequirementsTest.php
@@ -0,0 +1,42 @@
+<?php
+
+namespace Drupal\Tests\system\Functional\Update;
+
+use Drupal\Core\Url;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests system_requirements errors on update.php.
+ *
+ * @group Update
+ */
+class SystemRequirementsTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'system',
+  ];
+
+  /**
+   * Tests that for older versions of PHP a warning is shown.
+   */
+  public function testPhpWarning() {
+    $user = $this->drupalCreateUser(['administer software updates']);
+    $this->drupalLogin($user);
+    $url = Url::fromRoute('system.db_update');
+    $this->drupalGet($url);
+    $warning = sprintf('Your PHP installation is too old. Drupal requires at least PHP %s.', DRUPAL_MINIMUM_PHP);
+
+    if (version_compare(phpversion(), DRUPAL_MINIMUM_PHP) < 0) {
+      $this->assertText('Warnings found');
+      $this->assertText($warning);
+    }
+    else {
+      $this->assertNoText('Warnings found');
+      $this->assertNoText($warning);
+    }
+  }
+
+}