Qt 5.11 on Debian 9, cannot resolve SSLv3_client_method

[luca]

Hi all,
I'm building a very simple application using QSslSocket on a Debian Linux system.
When running the app I get:

qt.network.ssl: QSslSocket: cannot resolve SSLv3_client_method
qt.network.ssl: QSslSocket: cannot resolve SSLv3_server_method

It's probably because of a mismatch of OpenSSL version between Qt 5.11 build and my system.
I actually have libssl1.0 .
Even if it seems only a warning, I'd like to solve it.

How can I know what version was used for Qt 5.11 official build?

Thanks?