diff --git a/src/Symfony/Component/Cache/Simple/AbstractCache.php b/src/Symfony/Component/Cache/Simple/AbstractCache.php
index 732fa337da0d4..b0488075918e4 100644
--- a/src/Symfony/Component/Cache/Simple/AbstractCache.php
+++ b/src/Symfony/Component/Cache/Simple/AbstractCache.php
@@ -182,7 +182,7 @@ private function generateValues(iterable $values, array &$keys, $default): itera
         try {
             foreach ($values as $id => $value) {
                 if (!isset($keys[$id])) {
-                    $id = key($keys);
+                    throw new InvalidArgumentException(sprintf('Could not match value id "%s" to keys "%s".', $id, implode('", "', $keys)));
                 }
                 $key = $keys[$id];
                 unset($keys[$id]);
diff --git a/src/Symfony/Component/Cache/Traits/AbstractTrait.php b/src/Symfony/Component/Cache/Traits/AbstractTrait.php
index d4a16959a8cd9..2e7e2c89f6cbe 100644
--- a/src/Symfony/Component/Cache/Traits/AbstractTrait.php
+++ b/src/Symfony/Component/Cache/Traits/AbstractTrait.php
@@ -119,7 +119,7 @@ public function clear(/*string $prefix = ''*/)
                 }
             }
             $namespaceToClear = $this->namespace.$namespaceVersionToClear;
-            $namespaceVersion = substr_replace(base64_encode(pack('V', mt_rand())), static::NS_SEPARATOR, 5);
+            $namespaceVersion = strtr(substr_replace(base64_encode(pack('V', mt_rand())), static::NS_SEPARATOR, 5), '/', '_');
             try {
                 $cleared = $this->doSave([static::NS_SEPARATOR.$this->namespace => $namespaceVersion], 0);
             } catch (\Exception $e) {
@@ -268,7 +268,7 @@ private function getId($key): string
                     $this->namespaceVersion = $v;
                 }
                 if ('1'.static::NS_SEPARATOR === $this->namespaceVersion) {
-                    $this->namespaceVersion = substr_replace(base64_encode(pack('V', time())), static::NS_SEPARATOR, 5);
+                    $this->namespaceVersion = strtr(substr_replace(base64_encode(pack('V', time())), static::NS_SEPARATOR, 5), '/', '_');
                     $this->doSave([static::NS_SEPARATOR.$this->namespace => $this->namespaceVersion], 0);
                 }
             } catch (\Exception $e) {