diff --git a/lib/typeprof/core/ast/sig_type.rb b/lib/typeprof/core/ast/sig_type.rb
index 72bcde86..6033ebce 100644
--- a/lib/typeprof/core/ast/sig_type.rb
+++ b/lib/typeprof/core/ast/sig_type.rb
@@ -80,13 +80,13 @@ def attrs = { type_params:, block_required: }
 
     class SigTyNode < Node
       def covariant_vertex(genv, changes, subst)
-        vtx = changes.new_vertex(genv, self)
+        vtx = changes.new_covariant_vertex(genv, self)
         covariant_vertex0(genv, changes, vtx, subst)
         vtx
       end
 
       def contravariant_vertex(genv, changes, subst)
-        vtx = Vertex.new(self)
+        vtx = changes.new_contravariant_vertex(genv, self)
         contravariant_vertex0(genv, changes, vtx, subst)
         vtx
       end
@@ -98,7 +98,7 @@ def covariant_vertex0(genv, changes, vtx, subst)
       end
 
       def contravariant_vertex0(genv, changes, vtx, subst)
-        Source.new(genv.true_type, genv.false_type).add_edge(genv, vtx)
+        changes.add_edge(genv, Source.new(genv.true_type, genv.false_type), vtx)
       end
 
       def show
@@ -112,7 +112,7 @@ def covariant_vertex0(genv, changes, vtx, subst)
       end
 
       def contravariant_vertex0(genv, changes, vtx, subst)
-        Source.new(genv.nil_type).add_edge(genv, vtx)
+        changes.add_edge(genv, Source.new(genv.nil_type), vtx)
       end
 
       def show
@@ -126,7 +126,7 @@ def covariant_vertex0(genv, changes, vtx, subst)
       end
 
       def contravariant_vertex0(genv, changes, vtx, subst)
-        subst[:"*self"].add_edge(genv, vtx)
+        changes.add_edge(genv, subst[:"*self"], vtx)
       end
 
       def show
@@ -140,7 +140,7 @@ def covariant_vertex0(genv, changes, vtx, subst)
       end
 
       def contravariant_vertex0(genv, changes, vtx, subst)
-        Source.new(genv.obj_type).add_edge(genv, vtx)
+        changes.add_edge(genv, Source.new(genv.obj_type), vtx)
       end
 
       def show
@@ -181,7 +181,7 @@ def covariant_vertex0(genv, changes, vtx, subst)
       end
 
       def contravariant_vertex0(genv, changes, vtx, subst)
-        Source.new(Type::Bot.new(genv)).add_edge(genv, vtx)
+        changes.add_edge(genv, Source.new(Type::Bot.new(genv)), vtx)
       end
 
       def show
@@ -195,7 +195,7 @@ def covariant_vertex0(genv, changes, vtx, subst)
       end
 
       def contravariant_vertex0(genv, changes, vtx, subst)
-        subst[:"*instance"].add_edge(genv, vtx)
+        changes.add_edge(genv, subst[:"*instance"], vtx)
       end
 
       def show
@@ -209,7 +209,7 @@ def covariant_vertex0(genv, changes, vtx, subst)
       end
 
       def contravariant_vertex0(genv, changes, vtx, subst)
-        subst[:"*class"].add_edge(genv, vtx)
+        changes.add_edge(genv, subst[:"*class"], vtx)
       end
 
       def show
@@ -375,7 +375,7 @@ def contravariant_vertex0(genv, changes, vtx, subst)
         cpath = @static_ret.last.cpath
         return unless cpath
         mod = genv.resolve_cpath(cpath)
-        Source.new(Type::Singleton.new(genv, mod)).add_edge(genv, vtx)
+        changes.add_edge(genv, Source.new(Type::Singleton.new(genv, mod)), vtx)
       end
 
       def show
@@ -436,7 +436,7 @@ def contravariant_vertex0(genv, changes, vtx, subst)
         return unless cpath
         mod = genv.resolve_cpath(cpath)
         args = @args.map {|arg| arg.contravariant_vertex(genv, changes, subst) }
-        Source.new(Type::Instance.new(genv, mod, args)).add_edge(genv, vtx)
+        changes.add_edge(genv, Source.new(Type::Instance.new(genv, mod, args)), vtx)
       end
 
       def show
@@ -458,23 +458,23 @@ def initialize(raw_decl, lenv)
       def subnodes = { types: }
 
       def covariant_vertex0(genv, changes, vtx, subst)
-        unified_elem = Vertex.new(self) # TODO
+        unified_elem = changes.new_covariant_vertex(genv, [self, :Elem]) # TODO
         elems = @types.map do |type|
           nvtx = type.covariant_vertex(genv, changes, subst)
-          nvtx.add_edge(genv, unified_elem)
+          changes.add_edge(genv, nvtx, unified_elem)
           nvtx
         end
         changes.add_edge(genv, Source.new(Type::Array.new(genv, elems, genv.gen_ary_type(unified_elem))), vtx)
       end
 
       def contravariant_vertex0(genv, changes, vtx, subst)
-        unified_elem = Vertex.new(self)
+        unified_elem = changes.new_contravariant_vertex(genv, [self, :Elem]) # TODO
         elems = @types.map do |type|
           nvtx = type.contravariant_vertex(genv, changes, subst)
-          nvtx.add_edge(genv, unified_elem)
+          changes.add_edge(genv, nvtx, unified_elem)
           nvtx
         end
-        Source.new(Type::Array.new(genv, elems, genv.gen_ary_type(unified_elem))).add_edge(genv, vtx)
+        changes.add_edge(genv, Source.new(Type::Array.new(genv, elems, genv.gen_ary_type(unified_elem))), vtx)
       end
 
       def show
@@ -513,7 +513,7 @@ def covariant_vertex0(genv, changes, vtx, subst)
 
       def contravariant_vertex0(genv, changes, vtx, subst)
         raise "unknown type variable: #{ @var }" unless subst[@var]
-        Source.new(Type::Var.new(genv, @var, subst[@var])).add_edge(genv, vtx)
+        changes.add_edge(genv, Source.new(Type::Var.new(genv, @var, subst[@var])), vtx)
       end
 
       def show
@@ -537,7 +537,7 @@ def covariant_vertex0(genv, changes, vtx, subst)
 
       def contravariant_vertex0(genv, changes, vtx, subst)
         @type.contravariant_vertex0(genv, changes, vtx, subst)
-        Source.new(genv.nil_type).add_edge(genv, vtx)
+        changes.add_edge(genv, Source.new(genv.nil_type), vtx)
       end
 
       def show
@@ -576,7 +576,7 @@ def covariant_vertex0(genv, changes, vtx, subst)
       end
 
       def contravariant_vertex0(genv, changes, vtx, subst)
-        Source.new(get_type(genv)).add_edge(genv, vtx)
+        changes.add_edge(genv, Source.new(get_type(genv)), vtx)
       end
 
       def show
@@ -648,7 +648,7 @@ def contravariant_vertex0(genv, changes, vtx, subst)
         return unless cpath
         mod = genv.resolve_cpath(cpath)
         args = @args.map {|arg| arg.contravariant_vertex(genv, changes, subst) }
-        Source.new(Type::Instance.new(genv, mod, args)).add_edge(genv, vtx)
+        changes.add_edge(genv, Source.new(Type::Instance.new(genv, mod, args)), vtx)
       end
 
       def show
diff --git a/lib/typeprof/core/graph/box.rb b/lib/typeprof/core/graph/box.rb
index 496324c7..8f4d5eec 100644
--- a/lib/typeprof/core/graph/box.rb
+++ b/lib/typeprof/core/graph/box.rb
@@ -184,8 +184,7 @@ def resolve_overloads(changes, genv, node, param_map, a_args, ret)
       @method_types.each do |method_type|
         param_map0 = param_map.dup
         if method_type.type_params
-          method_type.type_params.map do |var|
-            vtx = Vertex.new(node)
+          method_type.type_params.zip(yield(method_type)) do |var, vtx|
             param_map0[var] = vtx
           end
         end
@@ -210,6 +209,7 @@ def resolve_overloads(changes, genv, node, param_map, a_args, ret)
           end
         end
         ret_vtx = method_type.return_type.covariant_vertex(genv, changes, param_map0)
+
         changes.add_edge(genv, ret_vtx, ret)
         match_any_overload = true
       end
@@ -644,6 +644,7 @@ def initialize(node, genv, recv, mid, a_args, subclasses)
       @a_args.block.add_edge(genv, self) if @a_args.block
       @ret = Vertex.new(node)
       @subclasses = subclasses
+      @generics = {}
     end
 
     attr_reader :recv, :mid, :ret
@@ -673,7 +674,9 @@ def run0(genv, changes)
                 ty_env[param] = arg
               end
             end
-            mdecl.resolve_overloads(changes, genv, @node, ty_env, @a_args, @ret)
+            mdecl.resolve_overloads(changes, genv, @node, ty_env, @a_args, @ret) do |method_type|
+              @generics[method_type] ||= method_type.type_params.map {|var| Vertex.new(@node) }
+            end
           end
         elsif !me.defs.empty?
           me.defs.each do |mdef|
diff --git a/lib/typeprof/core/graph/change_set.rb b/lib/typeprof/core/graph/change_set.rb
index a98b1a40..4a59c072 100644
--- a/lib/typeprof/core/graph/change_set.rb
+++ b/lib/typeprof/core/graph/change_set.rb
@@ -4,6 +4,7 @@ def initialize(node, target)
       @node = node
       @target = target
       @covariant_types = {}
+      @contravariant_types = {}
       @edges = []
       @new_edges = []
       @boxes = {}
@@ -44,11 +45,16 @@ def copy_from(other)
       other.diagnostics.clear
     end
 
-    def new_vertex(genv, sig_type_node)
+    def new_covariant_vertex(genv, sig_type_node)
       # This is used to avoid duplicated vertex generation for the same sig node
       @covariant_types[sig_type_node] ||= Vertex.new(sig_type_node)
     end
 
+    def new_contravariant_vertex(genv, sig_type_node)
+      # This is used to avoid duplicated vertex generation for the same sig node
+      @contravariant_types[sig_type_node] ||= Vertex.new(sig_type_node)
+    end
+
     def add_edge(genv, src, dst)
       raise src.class.to_s unless src.is_a?(BasicVertex)
       src.add_edge(genv, dst) if !@edges.include?([src, dst]) && !@new_edges.include?([src, dst])
diff --git a/lib/typeprof/core/graph/vertex.rb b/lib/typeprof/core/graph/vertex.rb
index b841fbb2..b39d8f8f 100644
--- a/lib/typeprof/core/graph/vertex.rb
+++ b/lib/typeprof/core/graph/vertex.rb
@@ -142,6 +142,7 @@ def initialize(origin)
       when RBS::AST::Declarations::Base
       when ValueEntity
       when ActualArguments
+      when Array
       else
         raise "unknown class: #{ origin.class }"
       end
diff --git a/scenario/misc/ivar-stuck-case.rb b/scenario/misc/ivar-stuck-case.rb
new file mode 100644
index 00000000..ed352532
--- /dev/null
+++ b/scenario/misc/ivar-stuck-case.rb
@@ -0,0 +1,12 @@
+## update: test.rbs
+class Foo
+  def check: [T] (T) -> [T]
+end
+
+## update: test.rb
+class Foo
+  def foo
+    @foo = []
+    @foo = check(@foo)
+  end
+end