I am upgrading from version 9.1.9 to 9.4.5

during the pg_upgrade process I execute the standard:

pg_upgrade -b <old bin dir> -B <new bin dir> -d <old data dir> -D <new data dir>

The process starts upgrading but breaks out on the following error:

pg_restore: creating FUNCTION get_index_keys("oid", "oid")
pg_restore: [archiver (db)] Error while PROCESSING TOC:
pg_restore: [archiver (db)] Error from TOC entry 2583; 1255 7687907 FUNCTION get_index_keys("oid", "oid") postgres
pg_restore: [archiver (db)] could not execute query: ERROR: could not find function "repack_get_index_keys" in file "/usr/local/pgsql-9.4.5/lib/pg_repack.so"
Command was: CREATE FUNCTION "get_index_keys"("oid", "oid") RETURNS "text"
LANGUAGE "c" STABLE STRICT
AS '$libdir/pg_repack', 're...

Does anyone know the cause and/or workaround for this issue?

Your assistance is greatly appreciated.