Gemfile in asciidoctor-epub3-1.5.0.alpha.13 vs Gemfile in asciidoctor-epub3-1.5.0.alpha.14

- old
+ new

@@ -3,10 +3,14 @@
 source 'https://rubygems.org'
 
 # Look in asciidoctor-epub3.gemspec for runtime and development dependencies.
 gemspec
 
-gem 'asciidoctor', ENV['ASCIIDOCTOR_VERSION'], require: false if ENV.key? 'ASCIIDOCTOR_VERSION'
+if ENV.key? 'ASCIIDOCTOR_VERSION'
+  gem 'asciidoctor', ENV['ASCIIDOCTOR_VERSION'], require: false
+  # Newer asciidoctor-diagram 1.5.x require asciidoctor >=1.5.7
+  gem 'asciidoctor-diagram', '1.5.16', require: false if Gem::Version.new(ENV['ASCIIDOCTOR_VERSION']) < Gem::Version.new('2.0.0')
+end
 
 group :optional do
   # epubcheck-ruby might be safe to be converted into runtime dependency, but could have issues when packaged into asciidoctorj-epub3
   gem 'epubcheck-ruby', '~> 4.2.2.0'
   # We would like to make kindlegen a runtime dependency, but can't because of the way asciidoctorj-epub3 packaging works