diff --git a/asciidoctor-pdf-gem-installer.pom b/asciidoctor-pdf-gem-installer.pom
index b77abef..e1fa53e 100644
--- a/asciidoctor-pdf-gem-installer.pom
+++ b/asciidoctor-pdf-gem-installer.pom
@@ -19,6 +19,9 @@
                 <artifactId>gem-maven-plugin</artifactId>
                 <version>1.1.8</version>
                 <extensions>true</extensions>
+                <configuration>
+                    <jrubyVersion>9.3.8.0</jrubyVersion>
+                </configuration>
             </plugin>
         </plugins>
     </build>
diff --git a/test-asciidoctor-upstream.sh b/test-asciidoctor-upstream.sh
index c3b897d..56912fd 100755
--- a/test-asciidoctor-upstream.sh
+++ b/test-asciidoctor-upstream.sh
@@ -29,9 +29,12 @@ cd ../..
 #rm -rf build/maven-pdf
 cd ..
 
+unset GEM_PATH GEM_HOME JRUBY_OPTS
+
 $GRADLE_CMD -S -Pskip.signing -PasciidoctorJVersion=${ASCIIDOCTORJ_VERSION:-2.5.2} \
                               -PasciidoctorPdfGemVersion=${ASCIIDOCTOR_PDF_VERSION}-SNAPSHOT \
                               -PprawnGemVersion=${PRAWN_VERSION:-2.4.0} \
                               -PuseMavenLocal=true \
+                              --no-daemon \
                               :asciidoctorj-pdf:clean :asciidoctorj-pdf:check
 exit $?