diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index bd7d49ef8b..c78540a486 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -19,13 +19,18 @@
 
 /**
  * Minimum supported version of PHP.
+ *
+ * Drupal cannot be installed on versions of PHP older than this version.
  */
 const DRUPAL_MINIMUM_PHP = '5.5.9';
 
 /**
  * Minimum recommended version of PHP.
+ *
+ * Sites installing Drupal on PHP versions lower than this will see a warning
+ * message, but Drupal can still be installed.
  */
-const DRUPAL_RECOMMENDED_PHP = '7.1.0';
+const DRUPAL_RECOMMENDED_PHP = '7.1.3';
 
 /**
  * Minimum recommended value of PHP memory_limit.
diff --git a/core/modules/simpletest/src/InstallerTestBase.php b/core/modules/simpletest/src/InstallerTestBase.php
index 04e94e82b7..57ca485fdb 100644
--- a/core/modules/simpletest/src/InstallerTestBase.php
+++ b/core/modules/simpletest/src/InstallerTestBase.php
@@ -200,10 +200,16 @@ protected function setUpSettings() {
 
   /**
    * Installer step: Requirements problem.
+   *
+   * Override this method to test specific requirements warnings or errors
+   * during the installer.
+   *
+   * @see system_requirements()
    */
   protected function setUpRequirementsProblem() {
     // By default, skip the "recommended PHP version" warning on older test
-    // environments.
+    // environments. This allows the installer to be tested consistently on
+    // both recommended PHP versions and older (but still supported) versions.
     if (version_compare(phpversion(), DRUPAL_RECOMMENDED_PHP) < 0) {
       $this->continueOnExpectedWarnings(['PHP']);
     }