diff --git a/Gemfile b/Gemfile
index faeae86..e133121 100644
--- a/Gemfile
+++ b/Gemfile
@@ -5,3 +5,4 @@ gemspec
 
 gem "rake", "~> 12.0"
 gem "rspec", "~> 3.0"
+gem "open-uri"
diff --git a/lib/mn2pdf.rb b/lib/mn2pdf.rb
index b3fb53d..af7e75e 100644
--- a/lib/mn2pdf.rb
+++ b/lib/mn2pdf.rb
@@ -5,7 +5,7 @@
 
 module Mn2pdf
   MN2PDF_JAR_PATH = File.join(File.dirname(__FILE__), "../bin/mn2pdf.jar")
-  DEFAULT_JAVA_OPTS = %w[-Xss5m -Xmx2048m -Djava.awt.headless=true].freeze
+  DEFAULT_JAVA_OPTS = %w[-Xss10m -Xmx3g -Djava.awt.headless=true].freeze
   FONTS_MANIFEST = :font_manifest
 
   def self.jvm_options