diff --git a/toy-impl/inference.py b/toy-impl/inference.py
index b77f3fa..9eab2e5 100644
--- a/toy-impl/inference.py
+++ b/toy-impl/inference.py
@@ -32,6 +32,8 @@ def find_subst(ctx: dict[str, Type],
                 else:
                     if a not in b.constraints:
                         return f"{b} cannot take value of {a}"
+            if b in a.get_vars():
+                return "Recursive type is not supported"
             sub[b.name] = a
             return sub
 
diff --git a/toy-impl/test_subst.py b/toy-impl/test_subst.py
index 7662195..575dc20 100644
--- a/toy-impl/test_subst.py
+++ b/toy-impl/test_subst.py
@@ -54,5 +54,6 @@ try_case(TupleType([X, X]), TupleType([X, Y]), {})
 try_case(TupleType([X, X]), TupleType([Y, Y]), {})
 try_case(TupleType([X, Y]), TupleType([X, X]), {})
 try_case(TupleType([X, Y]), X, {})
+try_case(TupleType([i32, Y]), X, {})
 
 
diff --git a/toy-impl/type_def.py b/toy-impl/type_def.py
index a2196de..262d408 100644
--- a/toy-impl/type_def.py
+++ b/toy-impl/type_def.py
@@ -2,6 +2,9 @@ class Type:
     def __eq__(self, other):
         return False
 
+    def get_vars(self):
+        return []
+
 
 class BotType:
     def __eq__(self, other):
@@ -38,6 +41,9 @@ class TypeVariable(Type):
     def __eq__(self, other):
         return isinstance(other, TypeVariable) and self.name == other.name
 
+    def get_vars(self):
+        return [self]
+
 
 class ClassType(Type):
     name: str
@@ -83,6 +89,15 @@ class ParametricType(Type):
                 return False
         return True
 
+    def get_vars(self):
+        result = []
+        for p in self.params:
+            vars = p.get_vars()
+            for v in vars:
+                if v not in result:
+                    result.append(v)
+        return result
+
 class ListType(ParametricType):
     def __init__(self, param: Type):
         super().__init__([param])