diff --git a/python/ql/test/library-tests/frameworks/flask/flask_subclass.py b/python/ql/test/library-tests/frameworks/flask/flask_subclass.py
new file mode 100644
index 00000000000..03199077989
--- /dev/null
+++ b/python/ql/test/library-tests/frameworks/flask/flask_subclass.py
@@ -0,0 +1,14 @@
+from flask import Flask
+
+
+class Sub(Flask):
+    def __init__(self, *args, **kwargs):
+        Flask.__init__(self, *args, **kwargs)
+
+
+app = Sub(__name__) # $ MISSING: instance
+
+
+@app.route("/")
+def hello():
+    return "world"
\ No newline at end of file