diff --git a/src/MemcacheBackend.php b/src/MemcacheBackend.php
index ff5cf31..c4f646d 100644
--- a/src/MemcacheBackend.php
+++ b/src/MemcacheBackend.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\memcache;
 
+use Drupal\Component\Utility\Crypt;
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\Core\Cache\CacheTagsChecksumInterface;
@@ -257,13 +258,21 @@ class MemcacheBackend implements CacheBackendInterface {
     $data = serialize($item->data);
     $pieces = str_split($data, static::MAX_CHUNK_SIZE);
 
+    // Add a unique identifier each time this function is invoked.  This
+    // prevents a race condition where two sets on the same multipart item can
+    // clobber each other's children.  With this seed, each time a multipart
+    // entry is created, they get a different CID.  The parent (multipart) entry
+    // does not inherit this unique identifier, so it is still addressable using
+    // the CID it was initially given.
+    $seed = Crypt::randomBytesBase64();
+
     $children = [];
 
     foreach ($pieces as $i => $chunk) {
       // Child items do not need tags or expire, since that data is carried by
       // the parent.
       $chunkItem = new \stdClass();
-      $chunkItem->cid = sprintf('%s.%d', $item->cid, $i);
+      $chunkItem->cid = sprintf('%s.%s.%d', $item->cid, $seed, $i);
       $chunkItem->data = $chunk;
       $chunkItem->created = $item->created;
       $children[] = $chunkItem;