diff --git a/src/SimpleCache/CacheProvider.php b/src/SimpleCache/CacheProvider.php
index d2cc676..c795702 100644
--- a/src/SimpleCache/CacheProvider.php
+++ b/src/SimpleCache/CacheProvider.php
@@ -58,6 +58,16 @@ public function set($key, $value, $ttl = null)
 
         $timestamp = time();
 
+        if (is_null($ttl)) {
+            $ttl = 0;
+
+        } elseif ($ttl instanceof DateInterval) {
+            $datetimeObj = new DateTime();
+            $datetimeObj->add($ttl);
+
+            $ttl = $datetimeObj->getTimestamp() - $timestamp;
+        }
+
         return $this->doSet($key, $value, $ttl, $timestamp);
     }
 
@@ -148,28 +158,21 @@ public function deleteMultiple($keys)
     /**
      * Check if the TTL is expired or not.
      *
-     * @param int|null|DateInterval $ttl       The time to live of a cached data.
-     * @param int                   $timestamp The unix timesamp that want to check.
+     * @param int $ttl       The time to live of a cached data.
+     * @param int $timestamp The unix timesamp that want to check.
      * 
      * @return bool
      */
-    protected function isExpired($ttl, int $timestamp): bool
+    protected function isExpired(int $ttl, int $timestamp): bool
     {
         $now = time();
 
-        if (is_null($ttl)) {
+        // If $ttl equal to 0 means that never expires.
+        if (empty($ttl)) {
             return false;
 
-        } elseif (is_integer($ttl) && ($now - $timestamp < $ttl)) {
+        } elseif ($now - $timestamp < $ttl) {
             return false;
-
-        } elseif ($ttl instanceof DateInterval) {
-            $datetimeObj = new DateTime();
-            $datetimeObj->add($ttl);
-
-            if ($now - $timestamp < $datetimeObj->getTimestamp()) {
-                return false;
-            }
         }
 
         return true;
diff --git a/src/SimpleCache/Driver/Redis.php b/src/SimpleCache/Driver/Redis.php
index 2a51f31..a1cc4e4 100644
--- a/src/SimpleCache/Driver/Redis.php
+++ b/src/SimpleCache/Driver/Redis.php
@@ -163,6 +163,10 @@ protected function doSet(string $key, $value, int $ttl, int $timestamp): bool
             'value'     => $value
         ];
 
+        if (empty($ttl)) {
+            $ttl = null;
+        }
+
         $result = $this->redis->set(
             $this->getKeyName($key),
             serialize($contents),
diff --git a/tests/SimpleCache/CacheTest.php b/tests/SimpleCache/CacheTest.php
index c3dd870..69cd35b 100644
--- a/tests/SimpleCache/CacheTest.php
+++ b/tests/SimpleCache/CacheTest.php
@@ -126,14 +126,8 @@ public function testIsExpired()
         $method = $reflection->getMethod('isExpired');
         $method->setAccessible(true);
 
-        // Test null
-        $result = $method->invokeArgs($cache, [null, $time]);
-        $this->assertFalse($result);
-
-        // Test DateInterval
-        $dateInterval = new DateInterval('PT5M');
-
-        $result = $method->invokeArgs($cache, [$dateInterval, $time]);
+        // Test zero
+        $result = $method->invokeArgs($cache, [0, $time]);
         $this->assertFalse($result);
     }
 
diff --git a/tests/SimpleCache/DriverIntegrationTestCase.php b/tests/SimpleCache/DriverIntegrationTestCase.php
index cbcb175..1240c27 100644
--- a/tests/SimpleCache/DriverIntegrationTestCase.php
+++ b/tests/SimpleCache/DriverIntegrationTestCase.php
@@ -12,6 +12,7 @@
 
 use Psr\SimpleCache\CacheInterface;
 use Shieldon\Test\SimpleCache\CacheTestCase;
+use DateInterval;
 use function method_exists;
 
 /**
@@ -42,7 +43,7 @@ public function testDriverCombinedTests()
         }
 
         // Test method `set()` and `get()`
-        $cache->set('foo', 'bar', 300);
+        $cache->set('foo', 'bar');
         $this->assertSame('bar', $cache->get('foo'));
 
         $cache->set('foo', 'bar bar', 300);
@@ -113,5 +114,15 @@ public function testDriverCacheExpired()
         sleep(6);
         $this->assertSame(null, $cache->get('foo'));
         $this->assertFalse($cache->has('foo'));
+
+        // Test DateInterval
+        $dateInterval = new DateInterval('PT2S');
+        $cache->set('fkk', 'bar', $dateInterval);
+        $this->assertSame('bar', $cache->get('fkk'));
+        $this->assertTrue($cache->has('fkk'));
+
+        sleep(3);
+        $this->assertSame(null, $cache->get('fkk'));
+        $this->assertFalse($cache->has('fkk'));
     }
 }
\ No newline at end of file