diff --git a/psalm.xml b/psalm.xml
index af5ec45274cf9d52c6c38cb11cb239ff80f23921..287c81de6c57d3b70a140cc8a78fe6b0d20dd58c 100644
--- a/psalm.xml
+++ b/psalm.xml
@@ -6,6 +6,7 @@
         <directory name="src" />
         <ignoreFiles>
             <directory name="tests" />
+            <directory name="vendor" />
         </ignoreFiles>
     </projectFiles>
     <issueHandlers>
diff --git a/tests/Base64Test.php b/tests/Base64Test.php
index 339f5d23fe70033f0611f3fcc5cc36dc8e9f72f5..c96468600754e3eab84daa9495a64fd30b1c1b92 100644
--- a/tests/Base64Test.php
+++ b/tests/Base64Test.php
@@ -84,6 +84,16 @@ class Base64Test extends TestCase
         }
     }
 
+    public function testIssue22()
+    {
+        // Non-strict: ok
+        Base64::decode('00==');
+
+        // Strict: not ok
+        $this->expectException(RangeException::class);
+        Base64::decode('00==', true);
+    }
+
     /**
      * @dataProvider canonicalDataProvider
      */