diff --git a/src/Symfony/Component/Cache/Adapter/AbstractAdapter.php b/src/Symfony/Component/Cache/Adapter/AbstractAdapter.php
index 12122b7c7f..d5156ad5f7 100644
--- a/src/Symfony/Component/Cache/Adapter/AbstractAdapter.php
+++ b/src/Symfony/Component/Cache/Adapter/AbstractAdapter.php
@@ -51,7 +51,7 @@ abstract class AbstractAdapter implements AdapterInterface, CacheInterface, Logg
                 // Detect wrapped values that encode for their expiry and creation duration
                 // For compactness, these values are packed in the key of an array using
                 // magic numbers in the form 9D-..-..-..-..-00-..-..-..-5F
-                if (\is_array($v) && 1 === \count($v) && 10 === \strlen($k = key($v)) && "\x9D" === $k[0] && "\0" === $k[5] && "\x5F" === $k[9]) {
+                if (\is_array($v) && 1 === \count($v) && 10 === \strlen($k = (string) key($v)) && "\x9D" === $k[0] && "\0" === $k[5] && "\x5F" === $k[9]) {
                     $item->value = $v[$k];
                     $v = unpack('Ve/Nc', substr($k, 1, -1));
                     $item->metadata[CacheItem::METADATA_EXPIRY] = $v['e'] + CacheItem::METADATA_EXPIRY_OFFSET;
diff --git a/src/Symfony/Component/Cache/Adapter/ProxyAdapter.php b/src/Symfony/Component/Cache/Adapter/ProxyAdapter.php
index 8fd6f47451..c9baa3ad39 100644
--- a/src/Symfony/Component/Cache/Adapter/ProxyAdapter.php
+++ b/src/Symfony/Component/Cache/Adapter/ProxyAdapter.php
@@ -59,7 +59,7 @@ class ProxyAdapter implements AdapterInterface, CacheInterface, PruneableInterfa
                 // Detect wrapped values that encode for their expiry and creation duration
                 // For compactness, these values are packed in the key of an array using
                 // magic numbers in the form 9D-..-..-..-..-00-..-..-..-5F
-                if (\is_array($v) && 1 === \count($v) && 10 === \strlen($k = key($v)) && "\x9D" === $k[0] && "\0" === $k[5] && "\x5F" === $k[9]) {
+                if (\is_array($v) && 1 === \count($v) && 10 === \strlen($k = (string) key($v)) && "\x9D" === $k[0] && "\0" === $k[5] && "\x5F" === $k[9]) {
                     $item->value = $v[$k];
                     $v = unpack('Ve/Nc', substr($k, 1, -1));
                     $item->metadata[CacheItem::METADATA_EXPIRY] = $v['e'] + CacheItem::METADATA_EXPIRY_OFFSET;
diff --git a/src/Symfony/Component/Cache/Tests/Adapter/AdapterTestCase.php b/src/Symfony/Component/Cache/Tests/Adapter/AdapterTestCase.php
index d7fe3ebc60..27354cf911 100644
--- a/src/Symfony/Component/Cache/Tests/Adapter/AdapterTestCase.php
+++ b/src/Symfony/Component/Cache/Tests/Adapter/AdapterTestCase.php
@@ -272,6 +272,30 @@ abstract class AdapterTestCase extends CachePoolTest
         $this->assertFalse($cache->hasItem('foobar'));
         $this->assertTrue($cache->hasItem('barfoo'));
     }
+
+    public function testWeirdDataMatchingMetadataWrappedValues()
+    {
+        if (isset($this->skippedTests[__FUNCTION__])) {
+            $this->markTestSkipped($this->skippedTests[__FUNCTION__]);
+        }
+
+        $cache = $this->createCachePool(0, __FUNCTION__);
+        $cache->clear();
+
+        $item = $cache->getItem('foobar');
+
+        // it should be an array containing only one element
+        // with key having a strlen of 10.
+        $weirdDataMatchingMedatataWrappedValue = [
+            1234567890 => [
+                1,
+            ],
+        ];
+
+        $cache->save($item->set($weirdDataMatchingMedatataWrappedValue));
+
+        $this->assertTrue($cache->hasItem('foobar'));
+    }
 }
 
 class NotUnserializable