diff --git a/midas/checker/dispatcher.py b/midas/checker/dispatcher.py
index fef6b04..77e1f45 100644
--- a/midas/checker/dispatcher.py
+++ b/midas/checker/dispatcher.py
@@ -258,6 +258,12 @@ class CallDispatcher(Generic[E]):
         """
         valid: bool = True
         for arg in arguments:
+            if arg.parameter.unsupported:
+                # Always report error
+                self.reporter.error(
+                    arg.arg_expr.location, f"Unsupported argument {arg.parameter.name}"
+                )
+
             if not self.types.is_subtype(arg.arg_type, arg.parameter.type):
                 if report_errors:
                     self.reporter.error(
diff --git a/midas/checker/types.py b/midas/checker/types.py
index f1b38f4..5b043bc 100644
--- a/midas/checker/types.py
+++ b/midas/checker/types.py
@@ -69,10 +69,14 @@ class Function:
         name: str
         type: Type
         required: bool
+        unsupported: bool = False
 
         def __str__(self) -> str:
             opt: str = "" if self.required else "?"
-            return f"{self.name}: {self.type}{opt}"
+            param: str = f"{self.name}: {self.type}{opt}"
+            if self.unsupported:
+                param = f"({param})"
+            return param
 
 
 @dataclass(frozen=True, kw_only=True)