diff --git a/lib/http/cookie_jar/abstract_store.rb b/lib/http/cookie_jar/abstract_store.rb
index 9c062ed..3a4594f 100644
--- a/lib/http/cookie_jar/abstract_store.rb
+++ b/lib/http/cookie_jar/abstract_store.rb
@@ -18,7 +18,7 @@ class HTTP::CookieJar::AbstractStore
         require 'http/cookie_jar/%s_store' % symbol
         @@class_map.fetch(symbol)
       rescue LoadError, IndexError => e
-        raise IndexError, 'cookie store unavailable: %s, error: %s' % symbol.inspect, e.message
+        raise IndexError, 'cookie store unavailable: %s, error: %s' % [symbol.inspect, e.message]
       end
     end
 
diff --git a/test/test_http_cookie_jar.rb b/test/test_http_cookie_jar.rb
index b84fcc6..969ee7f 100644
--- a/test/test_http_cookie_jar.rb
+++ b/test/test_http_cookie_jar.rb
@@ -9,6 +9,15 @@ module TestHTTPCookieJar
       }
     end
 
+    def test_nonexistent_store_in_config
+      assert_raise_with_message(
+        ArgumentError,
+        /cookie store unavailable: :nonexistent, error: cannot load .*nonexistent_store/
+      ) {
+        HTTP::CookieJar.new(store: :nonexistent)
+      }
+    end
+
     def test_erroneous_store
       Dir.mktmpdir { |dir|
         Dir.mkdir(File.join(dir, 'http'))