It turns out that I have a piece of software that I installed locally on my user space and it installed some libraries in `~/local/lib`. Within that directory, the software had installed `libQtCore.so.4` and `libQtGui.so.4`. This were the only Qt related libraries installed here. Likewise, I had set
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/home/path/to/user/local/lib
This meant that the linker found these libraries before the ones located in `/usr/lib64`. Changing $LD_LIBRARY_PATH so that it no longer points to `~/local/lib`, let the linker do its job and solved my problem.