Sorting bigger files gives segmentation fault

mkdir tmp
sort -u *.txt -T tmp/ -o output.txt

there are just a few few ten GByte sized files that needs to be sorted..

The problem is that after a few minutes sort gives a segmentation fault.

The OS is an up-to-date Scientific Linux 6.6.

Question: How can I "sort -u" the files? Sort cannot handle larger files?.. The RAM isn't half full when it segfaults.. only one core is on 100%