"mysqlpp::Connection: incomplete type"?

[Alex]

Here's my code:
mysqlpp::Connection awi_mysql_conn(false);

And here's what my compiler tells me:

./src/Definitions.cpp:35: error: variable âmysqlpp::Connection
                   awi_mysql_connâ has initializer but incomplete type

Would anyone happen to know what I'm doing wrong here? I did #include
"query.h" which should be enough, no?

Thanks in advance.