diff --git a/spec/pom.xml b/spec/pom.xml
index e87ba95..621a9a7 100644
--- a/spec/pom.xml
+++ b/spec/pom.xml
@@ -83,7 +83,7 @@
         <site.output.dir>${project.build.directory}/staging</site.output.dir>
         <maven.site.skip>true</maven.site.skip>
         <asciidoctorj.version>2.5.13</asciidoctorj.version>
-        <asciidoctorj.pdf.version>2.3.17</asciidoctorj.pdf.version>
+        <asciidoctorj.pdf.version>2.3.18</asciidoctorj.pdf.version>
         <jruby.version>9.3.15.0</jruby.version>
         <!-- status: DRAFT, BETA, etc., or blank for final -->
         <status>DRAFT</status>