diff --git a/common/functions.sh b/common/functions.sh
index c95817a..e0fa698 100644
--- a/common/functions.sh
+++ b/common/functions.sh
@@ -79,7 +79,7 @@ get_system_used_space() {
 }
 
 human_readable_bytes() {
-  local spacebytes="expr $1"
+  local spacebytes=$(printf -v int '%d\n' "$1" 2>/dev/null)
   spacekb=`expr "$spacebytes" / 1024`
   spacemb=`expr "$spacebytes" / 1024 / 1024`
   spacegb=`expr "$spacebytes" / 1024 / 1024 / 1024`