diff --git a/lib/Assert/Assertion.php b/lib/Assert/Assertion.php
index ea9bb9d2..7acdb2d4 100644
--- a/lib/Assert/Assertion.php
+++ b/lib/Assert/Assertion.php
@@ -1586,7 +1586,7 @@ public static function classExists($value, $message = null, $propertyPath = null
      */
     public static function interfaceExists($value, $message = null, $propertyPath = null)
     {
-        if (! class_exists($value)) {
+        if (! interface_exists($value)) {
             $message = sprintf(
                 $message ?: 'Interface "%s" does not exist.',
                 static::stringify($value)
diff --git a/tests/Assert/Tests/AssertTest.php b/tests/Assert/Tests/AssertTest.php
index cfd32c0c..4e2b844a 100644
--- a/tests/Assert/Tests/AssertTest.php
+++ b/tests/Assert/Tests/AssertTest.php
@@ -1444,8 +1444,7 @@ public function testInvalidInterfaceExists()
 
     public function testValidInterfaceExists()
     {
-        $this->setExpectedException('Assert\AssertionFailedException', null, Assertion::INVALID_INTERFACE);
-        Assertion::interfaceExists("\\Countable");
+        $this->assertTrue(Assertion::interfaceExists("\\Countable"));
     }
 
     /**