diff --git a/src/Symfony/Component/Cache/Adapter/AbstractAdapter.php b/src/Symfony/Component/Cache/Adapter/AbstractAdapter.php
index 883a94ba9bae8..6bfcb99ed2dcf 100644
--- a/src/Symfony/Component/Cache/Adapter/AbstractAdapter.php
+++ b/src/Symfony/Component/Cache/Adapter/AbstractAdapter.php
@@ -34,7 +34,7 @@ abstract class AbstractAdapter implements AdapterInterface, CacheInterface, Logg
 
     protected function __construct(string $namespace = '', int $defaultLifetime = 0)
     {
-        $this->namespace = '' === $namespace ? '' : CacheItem::validateKey($namespace).':';
+        $this->namespace = '' === $namespace ? '' : CacheItem::validateKey($namespace).'_';
         if (null !== $this->maxIdLength && \strlen($namespace) > $this->maxIdLength - 24) {
             throw new InvalidArgumentException(sprintf('Namespace must be %d chars max, %d given ("%s")', $this->maxIdLength - 24, \strlen($namespace), $namespace));
         }
diff --git a/src/Symfony/Component/Cache/Tests/Adapter/MaxIdLengthAdapterTest.php b/src/Symfony/Component/Cache/Tests/Adapter/MaxIdLengthAdapterTest.php
index fec985e6da994..f18437a29b495 100644
--- a/src/Symfony/Component/Cache/Tests/Adapter/MaxIdLengthAdapterTest.php
+++ b/src/Symfony/Component/Cache/Tests/Adapter/MaxIdLengthAdapterTest.php
@@ -26,8 +26,8 @@ public function testLongKey()
         $cache->expects($this->exactly(2))
             ->method('doHave')
             ->withConsecutive(
-                [$this->equalTo('----------:nWfzGiCgLczv3SSUzXL3kg:')],
-                [$this->equalTo('----------:---------------------------------------')]
+                [$this->equalTo('----------_nWfzGiCgLczv3SSUzXL3kg:')],
+                [$this->equalTo('----------_---------------------------------------')]
             );
 
         $cache->hasItem(str_repeat('-', 40));
@@ -46,7 +46,7 @@ public function testLongKeyVersioning()
         $reflectionMethod->setAccessible(true);
 
         // No versioning enabled
-        $this->assertEquals('--------------------------:------------', $reflectionMethod->invokeArgs($cache, [str_repeat('-', 12)]));
+        $this->assertEquals('--------------------------_------------', $reflectionMethod->invokeArgs($cache, [str_repeat('-', 12)]));
         $this->assertLessThanOrEqual(50, \strlen($reflectionMethod->invokeArgs($cache, [str_repeat('-', 12)])));
         $this->assertLessThanOrEqual(50, \strlen($reflectionMethod->invokeArgs($cache, [str_repeat('-', 23)])));
         $this->assertLessThanOrEqual(50, \strlen($reflectionMethod->invokeArgs($cache, [str_repeat('-', 40)])));
@@ -56,7 +56,7 @@ public function testLongKeyVersioning()
         $reflectionProperty->setValue($cache, true);
 
         // Versioning enabled
-        $this->assertEquals('--------------------------:1/------------', $reflectionMethod->invokeArgs($cache, [str_repeat('-', 12)]));
+        $this->assertEquals('--------------------------_1/------------', $reflectionMethod->invokeArgs($cache, [str_repeat('-', 12)]));
         $this->assertLessThanOrEqual(50, \strlen($reflectionMethod->invokeArgs($cache, [str_repeat('-', 12)])));
         $this->assertLessThanOrEqual(50, \strlen($reflectionMethod->invokeArgs($cache, [str_repeat('-', 23)])));
         $this->assertLessThanOrEqual(50, \strlen($reflectionMethod->invokeArgs($cache, [str_repeat('-', 40)])));