diff --git a/midas/checker/midas.py b/midas/checker/midas.py
index fabdd59..5e117c2 100644
--- a/midas/checker/midas.py
+++ b/midas/checker/midas.py
@@ -10,6 +10,7 @@ from midas.checker.reporter import FileReporter, Reporter
 from midas.checker.types import (
     AliasType,
     ComplexType,
+    ConstraintType,
     ExtensionType,
     Function,
     GenericType,
@@ -184,10 +185,10 @@ class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[None], m.Type.Visitor[Type
             return UnknownType()
 
     def visit_constraint_type(self, type: m.ConstraintType) -> Type:
-        type_: Type = type.type.accept(self)
-        type.constraint.accept(self)
-        # TODO
-        return UnknownType()
+        return ConstraintType(
+            type=type.type.accept(self),
+            constraint=type.constraint,
+        )
 
     def visit_complex_type(self, type: m.ComplexType) -> ComplexType:
         return ComplexType(
diff --git a/midas/checker/types.py b/midas/checker/types.py
index c16db79..f66468b 100644
--- a/midas/checker/types.py
+++ b/midas/checker/types.py
@@ -3,6 +3,9 @@ from __future__ import annotations
 from dataclasses import dataclass, field
 from typing import Optional, assert_never
 
+import midas.ast.midas as m
+from midas.ast.printer import MidasPrinter
+
 
 @dataclass(frozen=True, kw_only=True)
 class TopType:
@@ -130,6 +133,16 @@ class AppliedType:
         return f"{self.name}[{', '.join(map(str, self.args))}]"
 
 
+@dataclass(frozen=True, kw_only=True)
+class ConstraintType:
+    type: Type
+    constraint: m.Expr
+
+    def __str__(self) -> str:
+        printer = MidasPrinter()
+        return f"{self.type} where {printer.print(self.constraint)}"
+
+
 def substitute_typevars(type: Type, substitutions: dict[str, Type]) -> Type:
     def sub_argument(arg: Function.Argument):
         return Function.Argument(
@@ -195,6 +208,12 @@ def substitute_typevars(type: Type, substitutions: dict[str, Type]) -> Type:
                 body=substitute_typevars(body, substitutions),
             )
 
+        case ConstraintType():
+            return ConstraintType(
+                type=substitute_typevars(type.type, substitutions),
+                constraint=type.constraint,
+            )
+
         case TypeVar(name=name):
             if name in substitutions:
                 return substitutions[name]
@@ -238,4 +257,5 @@ Type = (
     | TypeVar
     | GenericType
     | AppliedType
+    | ConstraintType
 )
diff --git a/midas/generator/generator.py b/midas/generator/generator.py
index c7b1323..67e11e9 100644
--- a/midas/generator/generator.py
+++ b/midas/generator/generator.py
@@ -4,6 +4,7 @@ from dataclasses import dataclass, field
 from pathlib import Path
 from typing import Optional, assert_never
 
+import midas.ast.midas as m
 import midas.ast.python as p
 from midas.ast.location import Location
 from midas.checker.types import (
@@ -11,6 +12,7 @@ from midas.checker.types import (
     AppliedType,
     BaseType,
     ComplexType,
+    ConstraintType,
     ExtensionType,
     Function,
     GenericType,
@@ -308,6 +310,10 @@ class Generator(p.Stmt.Visitor[ast.stmt], p.Expr.Visitor[ast.expr]):
             case AppliedType(body=body):
                 self._make_cast_asserts(src_location, expr, body)
 
+            case ConstraintType(type=base, constraint=constraint):
+                self._make_cast_asserts(src_location, expr, base)
+                self._make_constraint_assert(src_location, expr, constraint)
+
             case TypeVar():
                 raise RuntimeError("Unexpected TypeVar")
 
@@ -347,3 +353,9 @@ class Generator(p.Stmt.Visitor[ast.stmt], p.Expr.Visitor[ast.expr]):
                 ast.Constant(f" to {type}"),
             ]
         )
+
+    def _make_constraint_assert(
+        self, src_location: Location, expr: ast.expr, constraint: m.Expr
+    ):
+        # TODO
+        pass