diff --git a/shard.yml b/shard.yml
index 984ae33..96b21f3 100644
--- a/shard.yml
+++ b/shard.yml
@@ -7,6 +7,10 @@ authors:
 
 crystal: ">= 0.23.1, < 2.0.0"
 
+dependencies:
+  json_mapping:
+    github: crystal-lang/json_mapping.cr
+
 development_dependencies:
   minitest:
     github: ysbaddaden/minitest.cr
diff --git a/src/webdriver/session/window.cr b/src/webdriver/session/window.cr
index e448647..cae6b5c 100644
--- a/src/webdriver/session/window.cr
+++ b/src/webdriver/session/window.cr
@@ -1,3 +1,5 @@
+require "json_mapping"
+
 module Selenium
   class Session
     class Window