chown: Invalid Argument

I'm trying to change ownership of some files from root to my user.
Most of my files belong to user oliversa and group of the same name:

-rw-r--r-- 1 oliversa oliversa 171B Dec 25 22:21 TODO
drwxr-xr-x 13 oliversa oliversa 442B Dec 31 11:31 code
drwxr-xr-x 5 oliversa oliversa 170B Dec 18 16:46 data
drwxr-xr-x 12 oliversa oliversa 408B Feb 22 17:47 design
drwxr-xr-x 9 oliversa oliversa 306B Dec 21 10:38 httpdocs
drwxr-xr-x 5 oliversa oliversa 170B Feb 27 19:33 script

I want to change these to be the same:
-rwxr-xr-x 1 root wheel 539B Dec 21 11:14 sync
-rw-r--r-- 1 root wheel 86B Dec 21 11:11 sync_files
-r-------- 1 root wheel 9B Dec 18 11:39 sync_pass

So I type:

$ chown oliversa:oliversa *
chown: oliversa: Invalid argument
$ sudo chown oliversa:oliversa *
Password:
chown: oliversa: Invalid argument

This is odd, I think.

Additionally oliversa doesn't exist in /etc/passwd:

$ grep oliversa /etc/passwd
$