Error make bottledwater: internal/pqexpbuffer.h: No such file or directory

[xrewndel]

I'm trying to make bottledwater-pg, here is output:

[root@bottledwater-pg]# make
make -C ext all
make[1]: Entering directory `/opt/bottledwater-pg/ext'
...
...
...

I/opt/postgresql/pg96/include/postgresql/server -I/opt/postgresql/pg96/include/postgresql/internal -I/opt/pgbin-build/pgbin/bin/../shared/linux_64/include -D_GNU_SOURCE -c -o snapshot.o snapshot.c
snapshot.c: In function ‘format_snapshot_row’:
snapshot.c:335:9: warning: format ‘%d’ expects argument of type ‘int’, but argument 3 has type ‘uint64’ [-Wformat=]
elog(ERROR, "Expected exactly 1 row from cursor, but got %d rows", SPI_processed);
^
gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -O2 -fpic -shared -o bottledwater.so io_util.o error_policy.o logdecoder.o oid2avro.o schema_cache.o protocol.o protocol_server.o snapshot.o -L/opt/postgresql/pg96/lib -Wl,-rpath,'/opt/pgbin-build/pgbin/bin/../shared/linux_64/lib' -L/opt/pgbin-build/pgbin/bin/../shared/linux_64/lib -Wl,--as-needed -Wl,-rpath,'/opt/postgresql/pg96/lib',--enable-new-dtags -L/opt/avro-c-1.8.1/build/avrolib/lib -lavro -lz -lsnappy

make[1]: Leaving directory /opt/bottledwater-pg/ext' make -C client all make[1]: Entering directory/opt/bottledwater-pg/client'
gcc -c -std=c99 -D_POSIX_C_SOURCE=200809L -I/opt/postgresql/pg96/include -I/opt/postgresql/pg96/include/postgresql/server -I/opt/avro-c-1.8.1/build/avrolib/include -I/usr/local/include -Wall -Wmissing-prototypes -Wpointer-arith -Wendif-labels -Wmissing-format-attribute -Wformat-security replication.c -o replication.o
replication.c:13:34: fatal error: internal/pqexpbuffer.h: No such file or directory
#include <internal/pqexpbuffer.h>
^
compilation terminated.
make[1]: *** [replication.o] Error 1
make[1]: Leaving directory `/opt/bottledwater-pg/client'
make: *** [all] Error 2

CentOS7, PostgreSQL 9.6, avro-c: 1.8.1

[xrewndel]

This happens while manual building.
I checked, I have pqexpbuffer.h in /opt/postgresql/pg96/include/postgresql/internal
which is included
-I/opt/postgresql/pg96/include
and in replication.c it is included also:
#include internal/pqexpbuffer.h

so, what is wrong? may be I should include it somehow explicit?