diff --git a/spec/ameba/ast/variabling/type_def_variable_spec.cr b/spec/ameba/ast/variabling/type_def_variable_spec.cr
new file mode 100644
index 00000000..7d273b1f
--- /dev/null
+++ b/spec/ameba/ast/variabling/type_def_variable_spec.cr
@@ -0,0 +1,30 @@
+require "../../../spec_helper"
+
+module Ameba::AST
+  describe TypeDecVariable do
+    var = Crystal::Var.new("foo")
+    declared_type = Crystal::Path.new("String")
+    type_dec = Crystal::TypeDeclaration.new(var, declared_type)
+
+    describe "#initialize" do
+      it "creates a new type dec variable" do
+        variable = TypeDecVariable.new(type_dec)
+        variable.node.should_not be_nil
+      end
+    end
+
+    describe "#name" do
+      it "returns var name" do
+        variable = TypeDecVariable.new(type_dec)
+        variable.name.should eq var.name
+      end
+
+      it "raises if type declaration is incorrect" do
+        type_dec = Crystal::TypeDeclaration.new(declared_type, declared_type)
+        expect_raises(Exception, "unsupported var node type: Crystal::Path") do
+          TypeDecVariable.new(type_dec).name
+        end
+      end
+    end
+  end
+end
diff --git a/src/ameba/ast/scope.cr b/src/ameba/ast/scope.cr
index 59c7f3de..8f930642 100644
--- a/src/ameba/ast/scope.cr
+++ b/src/ameba/ast/scope.cr
@@ -135,13 +135,13 @@ module Ameba::AST
 
     # Returns `true` if instance variable is assigned in this scope.
     def assigns_ivar?(name)
-      arguments.find(&.name.== name) &&
-        ivariables.find(&.name.== "@#{name}")
+      arguments.any?(&.name.== name) &&
+        ivariables.any?(&.name.== "@#{name}")
     end
 
     # Returns `true` if type declaration variable is assigned in this scope.
     def assigns_type_dec?(name)
-      type_dec_variables.find(&.name.== name) || outer_scope.try(&.assigns_type_dec?(name))
+      type_dec_variables.any?(&.name.== name) || outer_scope.try(&.assigns_type_dec?(name))
     end
 
     # Returns `true` if and only if current scope represents some
diff --git a/src/ameba/ast/variabling/type_def_variable.cr b/src/ameba/ast/variabling/type_def_variable.cr
index 9509eec4..e8ad83ae 100644
--- a/src/ameba/ast/variabling/type_def_variable.cr
+++ b/src/ameba/ast/variabling/type_def_variable.cr
@@ -13,16 +13,10 @@ module Ameba::AST
       var = @node.var
 
       case var
-      when Crystal::Var
-        var.name
-      when Crystal::InstanceVar
-        var.name
-      when Crystal::ClassVar
-        var.name
-      when Crystal::Global
+      when Crystal::Var, Crystal::InstanceVar, Crystal::ClassVar, Crystal::Global
         var.name
       else
-        raise "unsupported type declaration var node"
+        raise "unsupported var node type: #{var.class}"
       end
     end
   end