diff --git a/core/modules/simpletest/src/InstallerTestBase.php b/core/modules/simpletest/src/InstallerTestBase.php
index 73ca636132..151e9eff00 100644
--- a/core/modules/simpletest/src/InstallerTestBase.php
+++ b/core/modules/simpletest/src/InstallerTestBase.php
@@ -122,7 +122,7 @@ protected function setUp() {
     // Select profile.
     $this->setUpProfile();
 
-    // Skip the warning about old PHP, if applicable.
+    // Address the requirements problem screen, if any.
     $this->setUpRequirementsProblem();
 
     // Configure settings.
@@ -244,16 +244,14 @@ protected function continueOnExpectedWarnings($allowed_warnings = []) {
     if (strpos($this->getTextContent(), 'Errors found')) {
       return;
     }
-    $warning_elements = $this->cssSelect('.system-status-report__entry--warning summary');
-    // Don't allow more warnings than the ones permitted.
-    if (count($allowed_warnings) >= count($warning_elements)) {
-      $allowed_warning_list = implode(', ', $allowed_warnings);
+    $warning_elements = $this->cssSelect('h3#warning+details summary');
+    // Confirm that there are only the expected warnings.
+    if (count($allowed_warnings) == count($warning_elements)) {
+      $warnings = [];
       foreach ($warning_elements as $warning) {
-        $warning = trim((string) $warning);
-        if (!in_array($warning, $allowed_warnings, TRUE)) {
-          $this->fail("Warning '$warning' is not one of the allowed warnings ($allowed_warning_list)");
-        }
+        $warnings[] = trim((string) $warning);
       }
+      $this->assertEqual($allowed_warnings, $warnings);
       $this->clickLink('continue anyway');
     }
   }