diff --git a/introduction/important/building-notes.xml b/introduction/important/building-notes.xml
index bade697eb2..e7ae577eb9 100644
--- a/introduction/important/building-notes.xml
+++ b/introduction/important/building-notes.xml
@@ -364,7 +364,7 @@ systemd-run --user --pty --pipe --wait -G -d \
   sudo sh -c \
     "echo 0-3 > /sys/fs/cgroup/$$/cpuset.cpus"
   sudo sh -c \
-    "echo $((8 << 30)) > /sys/fs/cgroup/$$/memory.high"
+    "echo $(bc -e '8*2^30') > /sys/fs/cgroup/$$/memory.high"
   (
     sudo sh -c "echo $BASHPID > /sys/fs/cgroup/$$/cgroup.procs"
     exec make -j5
@@ -378,8 +378,9 @@ EOF</userinput></screen>
         <parameter>MemoryHigh=8G</parameter>
       </phrase>
       <phrase revision='sysv'>
-        <literal>8589934592</literal> (expanded from
-        <userinput>$((8 &lt;&lt; 30))</userinput>) in the
+        <literal>8589934592</literal> (the output of
+        <userinput>bc -e '8*2^30'</userinput>, 2^30 represents
+        2<superscript>30</superscript>, i.e. a Gigabyte) in the
         <filename>memory.high</filename> entry
       </phrase>, a soft limit of memory usage is set.
       If the processes in the cgroup (<command>make</command> and all the