diff --git a/core/lib/Drupal/Core/Cache/ChainedFastBackend.php b/core/lib/Drupal/Core/Cache/ChainedFastBackend.php
index 9f6be9d8ab..205a220a0f 100644
--- a/core/lib/Drupal/Core/Cache/ChainedFastBackend.php
+++ b/core/lib/Drupal/Core/Cache/ChainedFastBackend.php
@@ -300,7 +300,7 @@ protected function markAsOutdated() {
     // millisecond are invalidated. It is possible that caches will be later in
     // the same millisecond and are then incorrectly invalidated, but that only
     // costs one additional roundtrip to the persistent cache.
-    $now = round(microtime(TRUE) + .001, 3);
+    $now = round(microtime(TRUE) + .001, 4);
     if ($now > $this->getLastWriteTimestamp()) {
       $this->lastWriteTimestamp = $now;
       $this->consistentBackend->set(self::LAST_WRITE_TIMESTAMP_PREFIX . $this->bin, $this->lastWriteTimestamp);