  We present an extension to the gauge-invariant formulation of the
parameterized post-Newtonian (PPN) formalism, which allows its application to
symmetric teleparallel gravity theories. In its original formulation, the
gauge-invariant PPN formalism makes use of a gauge-invariant perturbative
expansion of tensor fields; however, one of the fundamental gravitational field
variables in symmetric teleparallel gravity theories is a flat, torsion-free
connection, hence not a tensor field. Since connections transform differently
from tensor fields under diffeomorphisms, we introduce here an adapted notion
of gauge-invariant perturbation variables for the symmetric teleparallel
connection, and show how the lowest order terms can be expressed in terms of
the common PPN potentials.
