diff --git a/artiq/compiler/builtins.py b/artiq/compiler/builtins.py
index 4e4406925..8ca095b81 100644
--- a/artiq/compiler/builtins.py
+++ b/artiq/compiler/builtins.py
@@ -71,11 +71,11 @@ class TException(types.TMono):
     def __init__(self, name="Exception"):
         super().__init__(name)
 
-class TIndexError(types.TMono):
+class TIndexError(TException):
     def __init__(self):
         super().__init__("IndexError")
 
-class TValueError(types.TMono):
+class TValueError(TException):
     def __init__(self):
         super().__init__("ValueError")
 
@@ -150,6 +150,9 @@ def is_range(typ, elt=None):
     else:
         return types.is_mono(typ, "range")
 
+def is_exception(typ):
+    return isinstance(typ.find(), TException)
+
 def is_iterable(typ):
     typ = typ.find()
     return isinstance(typ, types.TMono) and \
@@ -157,7 +160,7 @@ def is_iterable(typ):
 
 def get_iterable_elt(typ):
     if is_iterable(typ):
-        return typ.find()["elt"]
+        return typ.find()["elt"].find()
 
 def is_collection(typ):
     typ = typ.find()
diff --git a/artiq/compiler/transforms/inferencer.py b/artiq/compiler/transforms/inferencer.py
index 3db7e12c0..2e34c4e57 100644
--- a/artiq/compiler/transforms/inferencer.py
+++ b/artiq/compiler/transforms/inferencer.py
@@ -827,7 +827,7 @@ class Inferencer(algorithm.Visitor):
                         {"typeb": printer.name(typeb)},
                         locb)
                 ]
-            self._unify(node.name_type, node.filter.type.to_exception_type(),
+            self._unify(node.name_type, builtins.TException(node.filter.type.name),
                         node.name_loc, node.filter.loc, makenotes)
 
     def _type_from_arguments(self, node, ret):
diff --git a/artiq/compiler/types.py b/artiq/compiler/types.py
index 4b6dd9a55..b29eb513e 100644
--- a/artiq/compiler/types.py
+++ b/artiq/compiler/types.py
@@ -268,9 +268,6 @@ class TExceptionConstructor(TBuiltin):
     Note that this is not the same as the type of an instance of
     the class, which is ``TMono("Exception", ...)``.
     """
-    def to_exception_type(self):
-        # Exceptions currently can't have type parameters
-        return TMono(self.name, {})
 
 class TValue(Type):
     """