Ubuntu 16.04 build error !

[nightwalker89]

root@osboxes:~/chainstate# make
rm -f chainstate chainstate.o hex.o varint.o pubkey.o
g++ -Wall -I. -Ilibbase58 -Isecp256k1/include -Ibech32/ref/c -c -o chainstate.o chainstate.cc

g++ -Wall -I. -Ilibbase58 -Isecp256k1/include -Ibech32/ref/c -c -o hex.o hex.cc
g++ -Wall -I. -Ilibbase58 -Isecp256k1/include -Ibech32/ref/c -c -o varint.o varint.cc
varint.cc:5:1: error: ‘uint64_t’ does not name a type
uint64_t read_varint(uint64_t n)
^
varint.cc:24:1: error: ‘uint64_t’ does not name a type
uint64_t get_next_varint(string& str)
^
varint.cc:44:1: error: ‘uint64_t’ does not name a type
uint64_t decompress_amount(uint64_t x)
^
Makefile:14: recipe for target 'varint.o' failed
make: *** [varint.o] Error 1