[C++] Compilation failure size_t

$ uname -a
Linux edf2927682ca 5.3.0-40-generic #32-Ubuntu SMP Fri Jan 31 20:24:34 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
$ gcc --version
gcc (GCC) 10.0.1 20200220 (experimental)

g++  -DAVRO_SOURCE -I/home/docker/development/opensource-pack-builder/components/avro/BUILD/avro-src-1.9.2/lang/c++/api -I/home/docker/development/opensource-pack-builder/components/avro/BUILD/avro-src-1.9.2/lang/c++/build -I/home/docker/development/opensource-pack-builder/components/avro/DEPS/osp/Boost/latest/osp/include  -DNDEBUG -O3 -std=gnu++2a -fno-working-directory -ggdb3 -flto -ffat-lto-objects -fuse-linker-plugin -Wall -O3 -DNDEBUG   -std=c++11 -fPIC -o CMakeFiles/avrocpp_s.dir/impl/Zigzag.cc.o -c /home/docker/development/opensource-pack-builder/components/avro/BUILD/avro-src-1.9.2/lang/c++/impl/Zigzag.cc

In file included from /home/docker/development/opensource-pack-builder/components/avro/BUILD/avro-src-1.9.2/lang/c++/impl/Zigzag.cc:20:
/home/docker/development/opensource-pack-builder/components/avro/BUILD/avro-src-1.9.2/lang/c++/api/Zigzag.hh:37:11: error: 'size_t' does not name a type
 37 | AVRO_DECL size_t encodeInt32(int32_t input, std::array<uint8_t, 5> &output);
 | ^~~~~~
/home/docker/development/opensource-pack-builder/components/avro/BUILD/avro-src-1.9.2/lang/c++/api/Zigzag.hh:26:1: note: 'size_t' is defined in header '<cstddef>'; did you forget to '#include <cstddef>'?
 25 | #include "Config.hh"
 +++ |+#include <cstddef>
 26 | /// \file
/home/docker/development/opensource-pack-builder/components/avro/BUILD/avro-src-1.9.2/lang/c++/api/Zigzag.hh:38:11: error: 'size_t' does not name a type
 38 | AVRO_DECL size_t encodeInt64(int64_t input, std::array<uint8_t, 10> &output);
 | ^~~~~~
/home/docker/development/opensource-pack-builder/components/avro/BUILD/avro-src-1.9.2/lang/c++/api/Zigzag.hh:38:11: note: 'size_t' is defined in header '<cstddef>'; did you forget to '#include <cstddef>'?