segmentation fault when building postgres GiST index - postgresql

Question

I'm using postgres 9.4 on Ubuntu 14.04 LTS.
When I execute this query:
create index a_idx on my_table using gist(my_column);
I'm getting error:
erver closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: Failed.
!>
In the logs I can see this:
2016-04-21 11:30:11 BST LOG: server process (PID 7850) was terminated by signal 11: Segmentation fault
I checked if this column has any null values but it doesn't.
How can I debug this?
The structure of my_table is:
Table "public.my_table"
Column | Type | Modifiers | Storage | Stats target | Description
-----------+---------+-----------+----------+--------------+-------------
id | integer | not null | plain | |
my_column | bfp | | extended | |