-FILES=`find $RUNTESTS_SRC -type f -mtime +1 | head -n $COUNT`
-[ -z "$FILES" ] && error "No unchanged files - is $RUNTESTS_SRC a new dir?"
+FILES=$TMP/runtests.files
+# use "NUL" instead of newline as filename terminator, bug 19702
+find $RUNTESTS_SRC -type f -mtime +1 | head -n $COUNT | tr '\n' '\0' > $FILES
+[ -s "$FILES" ] ||
+ error "$RUNTESTS_SRC contains only files modifed less than 2 days ago"
+COUNT=$(xargs -0 -n 1 echo < $FILES | wc -l)
+
+log "copying $COUNT files from $RUNTESTS_SRC to $DST$RUNTESTS_SRC at `date`"
+tar cf - --null --files-from $FILES | tar xvf - -C $DST > /dev/null ||
+ error "copying $RUNTESTS_SRC" 11