diff --git a/hypnotoad/cases/torpex.py b/hypnotoad/cases/torpex.py
index d03f8a7b..14370955 100644
--- a/hypnotoad/cases/torpex.py
+++ b/hypnotoad/cases/torpex.py
@@ -206,6 +206,9 @@ def __init__(self, equilibOptions, meshOptions):
                         "direction of plasma current should be clockwise to be "
                         "consistent with sign of grad(psi)"
                     )
+
+            self.f_psi_sign = numpy.sign(psi_bndry - psi_axis)
+
             # index of a point close to the magnetic axis
             i_axis = numpy.searchsorted(R, R_axis)
             j_axis = numpy.searchsorted(Z, Z_axis)