diff --git a/src/Composer/Util/SpdxLicenseIdentifier.php b/src/Composer/Util/SpdxLicenseIdentifier.php
index 1ef896460..02525bb24 100644
--- a/src/Composer/Util/SpdxLicenseIdentifier.php
+++ b/src/Composer/Util/SpdxLicenseIdentifier.php
@@ -40,18 +40,19 @@ class SpdxLicenseIdentifier
     public function validate($license)
     {
         if (is_array($license)) {
-            $license = count($license) > 1 ? '('.implode(' or ', $license).')' : reset($license);
+            $count = count($license);
+            if ($count !== count(array_filter($license, 'is_string'))) {
+                throw new \InvalidArgumentException('Array of strings expected.');
+            }
+            $license = $count > 1  ? '('.implode(' or ', $license).')' : (string) reset($license);
         }
         if (!is_string($license)) {
             throw new \InvalidArgumentException(sprintf(
                 'Array or String expected, %s given.', gettype($license)
             ));
         }
-        if (!$this->isValidLicenseString($license)) {
-            return false;
-        }
 
-        return true;
+        return $this->isValidLicenseString($license);
     }
 
     /**
diff --git a/tests/Composer/Test/Util/SpdxLicenseIdentifierTest.php b/tests/Composer/Test/Util/SpdxLicenseIdentifierTest.php
index 9e4d1dd3b..4b461d31f 100644
--- a/tests/Composer/Test/Util/SpdxLicenseIdentifierTest.php
+++ b/tests/Composer/Test/Util/SpdxLicenseIdentifierTest.php
@@ -32,6 +32,7 @@ class SpdxLicenseIdentifierTest extends TestCase
     {
         return array(
             array(""),
+            array(array()),
             array("The system pwns you"),
             array("()"),
             array("(MIT)"),
@@ -50,6 +51,17 @@ class SpdxLicenseIdentifierTest extends TestCase
         );
     }
 
+    public static function provideInvalidArgument()
+    {
+        return array(
+            array(null),
+            array(new \stdClass),
+            array(array(new \stdClass)),
+            array(array("mixed", new \stdClass)),
+            array(array(new \stdClass, new \stdClass)),
+        );
+    }
+
     /**
      * @dataProvider provideValidLicenses
      * @param $license
@@ -71,11 +83,12 @@ class SpdxLicenseIdentifierTest extends TestCase
     }
 
     /**
+     * @dataProvider provideInvalidArgument
      * @expectedException InvalidArgumentException
      */
-    public function testInvalidArgument()
+    public function testInvalidArgument($invalidArgument)
     {
         $validator = new SpdxLicenseIdentifier();
-        $validator->validate(null);
+        $validator->validate($invalidArgument);
     }
 }
\ No newline at end of file