diff --git a/asciidoctorj-pdf/build.gradle b/asciidoctorj-pdf/build.gradle
index dafe3ed..68bfe20 100644
--- a/asciidoctorj-pdf/build.gradle
+++ b/asciidoctorj-pdf/build.gradle
@@ -26,6 +26,7 @@ dependencies {
   gems "rubygems:public_suffix:$public_suffixVersion"
   gems "rubygems:text-hyphen:$textHyphenVersion"
   gems "rubygems:ttfunk:$ttfunkGemVersion"
+  gems "rubygems:css_parser:$cssParserGemVersion"
 
   testImplementation "org.apache.pdfbox:pdfbox:$pdfboxVersion"
 }
diff --git a/build.gradle b/build.gradle
index 411973b..c571592 100644
--- a/build.gradle
+++ b/build.gradle
@@ -51,6 +51,7 @@ ext {
   spockVersion = '0.7-groovy-2.0'
   threadSafeGemVersion = '0.3.6'
   ttfunkGemVersion = '1.7.0'
+  cssParserGemVersion = '1.12.0'
   textHyphenVersion='1.4.1'
 }