diff -r 31633e503c17 -r a1b779ee035c etc/settings
--- a/etc/settings	Sun Nov 22 20:53:38 2015 +0100
+++ b/etc/settings	Sun Nov 22 23:13:02 2015 +0100
@@ -14,7 +14,7 @@
 
 ISABELLE_SCALA_BUILD_OPTIONS="-encoding UTF-8 -nowarn -target:jvm-1.7 -Xmax-classfile-name 130"
 
-ISABELLE_JAVA_SYSTEM_OPTIONS="-server -Dfile.encoding=UTF-8 -Disabelle.threads=0"
+ISABELLE_JAVA_SYSTEM_OPTIONS="-server -XX:+UseConcMarkSweepGC -XX:+CMSParallelRemarkEnabled -Dfile.encoding=UTF-8 -Disabelle.threads=0"
 
 classpath "$ISABELLE_HOME/lib/classes/Pure.jar"