diff --git a/Gemfile b/Gemfile
index d3c7840..4c3adcb 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,8 +1,8 @@
 
 gem "rake", "~> 13.0"
 
-gem "asciidoctor-pdf", "~> 1.5"
+gem "asciidoctor-pdf", "~> 1.6", ">= 1.6.0"
 
-gem "asciidoctor-diagram", "~> 2.1"
+gem "asciidoctor-diagram", "~> 2.2", ">= 2.2.0"
 
 gem "listen", "~> 3.4"