diff --git a/lib/rack/attack/store_proxy.rb b/lib/rack/attack/store_proxy.rb
index d88ad67..4d69853 100644
--- a/lib/rack/attack/store_proxy.rb
+++ b/lib/rack/attack/store_proxy.rb
@@ -3,26 +3,30 @@ module Rack
     module StoreProxy
       PROXIES = [DalliProxy, MemCacheProxy, RedisStoreProxy]
 
-      def self.build(store)
-        # RedisStore#increment needs different behavior, so detect that
-        # (method has an arity of 2; must call #expire separately
-        if (defined?(::ActiveSupport::Cache::RedisStore) && store.is_a?(::ActiveSupport::Cache::RedisStore)) ||
-          (defined?(::ActiveSupport::Cache::MemCacheStore) && store.is_a?(::ActiveSupport::Cache::MemCacheStore))
+      ACTIVE_SUPPORT_WRAPPER_CLASSES = Set.new(['ActiveSupport::Cache::MemCacheStore', 'ActiveSupport::Cache::RedisStore']).freeze
+      ACTIVE_SUPPORT_CLIENTS = Set.new(['Redis::Store', 'Dalli::Client', 'MemCache']).freeze
 
-          # ActiveSupport::Cache::RedisStore doesn't expose any way to set an expiry,
-          # so use the raw Redis::Store instead.
-          # We also want to use the underlying Dalli client instead of ::ActiveSupport::Cache::MemCacheStore,
-          # and the MemCache client if using Rails 3.x
-          client = store.instance_variable_get(:@data)
-          if (defined?(::Redis::Store) && client.is_a?(Redis::Store)) ||
-            (defined?(Dalli::Client) && client.is_a?(Dalli::Client)) || (defined?(MemCache) && client.is_a?(MemCache))
-            store = store.instance_variable_get(:@data)
-          end
-        end
-        klass = PROXIES.find { |proxy| proxy.handle?(store) }
-        klass ? klass.new(store) : store
+      def self.build(store)
+        client = unwrap_active_support_stores(store)
+        klass = PROXIES.find { |proxy| proxy.handle?(client) }
+        klass ? klass.new(client) : client
       end
 
+
+      private
+      def self.unwrap_active_support_stores(store)
+        # ActiveSupport::Cache::RedisStore doesn't expose any way to set an expiry,
+        # so use the raw Redis::Store instead.
+        # We also want to use the underlying Dalli client instead of ::ActiveSupport::Cache::MemCacheStore,
+        # and the MemCache client if using Rails 3.x
+
+        client = store.instance_variable_get(:@data)
+        if ACTIVE_SUPPORT_WRAPPER_CLASSES.include?(store.class.to_s) && ACTIVE_SUPPORT_CLIENTS.include?(client.class.to_s)
+          client
+        else
+          store
+        end
+      end
     end
   end
 end