diff --git a/core/lib/Drupal/Core/Routing/RouteBuilder.php b/core/lib/Drupal/Core/Routing/RouteBuilder.php
index a4b17e2..c3809db 100644
--- a/core/lib/Drupal/Core/Routing/RouteBuilder.php
+++ b/core/lib/Drupal/Core/Routing/RouteBuilder.php
@@ -121,6 +121,22 @@ public function __construct(MatcherDumperInterface $dumper, LockBackendInterface
   }
 
   /**
+   * Refreshes the local cache and rechecks if a rebuild is needed.
+   *
+   * @return bool
+   *   TRUE if the rebuild is needed, FALSE otherwise.
+   */
+  protected function isRebuildNeededUncached() {
+    // To absolutely ensure that the router rebuild is required, reset the cache
+    // in case they were set by another process.
+    $this->routeBuilderIndicator->resetCache();
+    if ($this->routeBuilderIndicator->isRebuildNeeded()) {
+      return TRUE;
+    }
+    return FALSE;
+  }
+
+  /**
    * {@inheritdoc}
    */
   public function rebuild() {
@@ -133,6 +149,11 @@ public function rebuild() {
       // We choose to block here since otherwise the routes might not be
       // available, resulting in a 404.
       $this->lock->wait('router_rebuild');
+
+      if ($this->isRebuildNeededUncached()) {
+        $this->rebuild();
+      }
+
       return FALSE;
     }
 
@@ -215,6 +236,9 @@ public function getCollectionDuringRebuild() {
    */
   public function rebuildIfNeeded() {
     if ($this->routeBuilderIndicator->isRebuildNeeded()) {
+      if (!$this->isRebuildNeededUncached()) {
+        return FALSE;
+      }
       return $this->rebuild();
     }
     return FALSE;
diff --git a/core/lib/Drupal/Core/Routing/RouteBuilderIndicator.php b/core/lib/Drupal/Core/Routing/RouteBuilderIndicator.php
index 5f06120..5cff225 100644
--- a/core/lib/Drupal/Core/Routing/RouteBuilderIndicator.php
+++ b/core/lib/Drupal/Core/Routing/RouteBuilderIndicator.php
@@ -34,6 +34,13 @@ public function __construct(StateInterface $state) {
   /**
    * {@inheritdoc}
    */
+  public function resetCache() {
+    $this->state->resetCache();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   public function setRebuildNeeded() {
     $this->state->set(static::REBUILD_NEEDED, TRUE);
   }
diff --git a/core/lib/Drupal/Core/Routing/RouteBuilderIndicatorInterface.php b/core/lib/Drupal/Core/Routing/RouteBuilderIndicatorInterface.php
index 68ce5b8..da9f97b 100644
--- a/core/lib/Drupal/Core/Routing/RouteBuilderIndicatorInterface.php
+++ b/core/lib/Drupal/Core/Routing/RouteBuilderIndicatorInterface.php
@@ -15,6 +15,11 @@
   const REBUILD_NEEDED = 'router_rebuild_needed';
 
   /**
+   * Reset the router builder indicator cache.
+   */
+  public function resetCache();
+
+  /**
    * Sets the router to be rebuilt next time the kernel is terminated.
    *
    * @see \Drupal\Core\EventSubscriber\RouterRebuildSubscriber::onKernelTerminate()
diff --git a/core/tests/Drupal/Tests/Core/Routing/RouteBuilderTest.php b/core/tests/Drupal/Tests/Core/Routing/RouteBuilderTest.php
index b0efe77..5e50083 100644
--- a/core/tests/Drupal/Tests/Core/Routing/RouteBuilderTest.php
+++ b/core/tests/Drupal/Tests/Core/Routing/RouteBuilderTest.php
@@ -278,9 +278,9 @@ public function testRebuildIfNecessary() {
     $this->routeBuilderIndicator->expects($this->once())
                 ->method('setRebuildDone');
 
-    $this->routeBuilderIndicator->expects($this->exactly(2))
+    $this->routeBuilderIndicator->expects($this->exactly(3))
                 ->method('isRebuildNeeded')
-                ->will($this->onConsecutiveCalls(TRUE, FALSE));
+                ->will($this->onConsecutiveCalls(TRUE, TRUE, FALSE));
 
     $this->yamlDiscovery->expects($this->any())
                         ->method('findAll')