diff --git a/core/lib/Drupal.php b/core/lib/Drupal.php
index 58c0c7f..1a63bb0 100644
--- a/core/lib/Drupal.php
+++ b/core/lib/Drupal.php
@@ -82,7 +82,8 @@ class Drupal {
   /**
    * The current system version.
    */
-  const VERSION = '8.9.0-dev';
+  // For testing only, force to a lower version number.
+  const VERSION = '8.8.0';
 
   /**
    * Core API compatibility.
diff --git a/core/modules/update/src/ProjectCoreCompatibility.php b/core/modules/update/src/ProjectCoreCompatibility.php
index 3940acd..551e9c7 100644
--- a/core/modules/update/src/ProjectCoreCompatibility.php
+++ b/core/modules/update/src/ProjectCoreCompatibility.php
@@ -235,6 +235,8 @@ protected function createMessageFromCoreCompatibility($core_compatibility_constr
    *   version of Drupal core, otherwise FALSE.
    */
   protected function isCoreCompatible($core_compatibility_constraint) {
+    // For testing only.
+    return FALSE;
     return Semver::satisfies($this->existingCoreVersion, $core_compatibility_constraint);
   }