diff --git a/varlink/scanner.py b/varlink/scanner.py
index b9c98e1..f1c766b 100644
--- a/varlink/scanner.py
+++ b/varlink/scanner.py
@@ -291,7 +291,7 @@ def filter_params(self, parent_name, varlink_type, _namespaced, args, kwargs):
                     )
                 return args
             else:
-                InvalidParameter(parent_name)
+                raise InvalidParameter(parent_name)
 
         if isinstance(varlink_type, _CustomType):
             # print("CustomType", varlink_type.name)
@@ -307,7 +307,8 @@ def filter_params(self, parent_name, varlink_type, _namespaced, args, kwargs):
             return args
 
         if isinstance(varlink_type, _Enum) and isinstance(args, str):
-            # print("Returned str:", args)
+            if args not in varlink_type.fields:
+                raise InvalidParameter(parent_name)
             return args
 
         if isinstance(varlink_type, _Array):
diff --git a/varlink/tests/test_scanner.py b/varlink/tests/test_scanner.py
index cb4e95e..4beee24 100755
--- a/varlink/tests/test_scanner.py
+++ b/varlink/tests/test_scanner.py
@@ -121,3 +121,19 @@ def test_interfacename(self):
         self.assertIsNotNone(
             varlink.Interface("interface xn--c1yn36f.xn--c1yn36f.xn--c1yn36f\nmethod F()->()").name
         )
+
+    def test_bad_types(self):
+        interface = varlink.Interface("""
+        interface org.example.testerrors
+        type TypeEnum ( a, b, c )
+        type TypeDict (dict: [string]string)
+
+        method Foo(param: TypeEnum) -> ()
+        method Bar(param: TypeDict) -> ()
+        """)
+        foo = interface.get_method("Foo")
+        with self.assertRaises(varlink.InvalidParameter):
+            interface.filter_params("test.call", foo.in_type, False, (), {"param": "d"})
+        bar = interface.get_method("Bar")
+        with self.assertRaises(varlink.InvalidParameter):
+            interface.filter_params("test.call", bar.in_type, False, (), {"param": {"dict": [1, 2, 3]}})