diff --git a/spec/pom.xml b/spec/pom.xml
index 9f42812..6f7a06f 100644
--- a/spec/pom.xml
+++ b/spec/pom.xml
@@ -89,7 +89,7 @@
         <site.output.dir>${project.build.directory}/staging</site.output.dir>
         <maven.site.skip>true</maven.site.skip>
         <asciidoctorj.version>3.0.0</asciidoctorj.version>
-        <asciidoctorj.pdf.version>2.3.20</asciidoctorj.pdf.version>
+        <asciidoctorj.pdf.version>2.3.21</asciidoctorj.pdf.version>
         <jruby.version>10.0.2.0</jruby.version>
         <!-- status: DRAFT, BETA, etc., or blank for final -->
         <status>DRAFT</status>