diff --git a/app/controllers/reactions_controller.rb b/app/controllers/reactions_controller.rb
index 350df903..5e0384e7 100644
--- a/app/controllers/reactions_controller.rb
+++ b/app/controllers/reactions_controller.rb
@@ -15,9 +15,8 @@ class ReactionsController < ApplicationController
 
   def create
     params.require :id
-    params.require :type
 
-    target = params[:type].constantize.find_by!(id: params[:id])
+    target = target_class.find_by!(id: params[:id])
 
     UseCase::Reaction::Create.call(
       source_user: current_user,
@@ -40,9 +39,8 @@ class ReactionsController < ApplicationController
 
   def destroy
     params.require :id
-    params.require :type
 
-    target = params[:type].constantize.find_by!(id: params[:id])
+    target = target_class.find_by!(id: params[:id])
 
     UseCase::Reaction::Destroy.call(
       source_user: current_user,
@@ -62,4 +60,16 @@ class ReactionsController < ApplicationController
       format.html { redirect_back(fallback_location: root_path) }
     end
   end
+
+  private
+
+  ALLOWED_TYPES = %w[Answer Comment].freeze
+  private_constant :ALLOWED_TYPES
+
+  def target_class
+    params.require :type
+    raise NameError unless ALLOWED_TYPES.include?(params[:type])
+
+    params[:type].constantize
+  end
 end