diff --git a/core/include/traccc/fitting/kalman_filter/two_filters_smoother.hpp b/core/include/traccc/fitting/kalman_filter/two_filters_smoother.hpp
index a523f47f5..8b4d1e3bd 100644
--- a/core/include/traccc/fitting/kalman_filter/two_filters_smoother.hpp
+++ b/core/include/traccc/fitting/kalman_filter/two_filters_smoother.hpp
@@ -149,6 +149,10 @@ struct two_filters_smoother {
         const matrix_type<1, 1> chi2 =
             matrix::transpose(residual) * matrix::inverse(R) * residual;
 
+        // Update the bound track parameters
+        bound_params.set_vector(filtered_vec);
+        bound_params.set_covariance(filtered_cov);
+
         // Return false if track is parallel to z-axis or phi is not finite
         const scalar theta = bound_params.theta();
         if (theta <= 0.f || theta >= constant<traccc::scalar>::pi) {
@@ -159,9 +163,9 @@ struct two_filters_smoother {
             return kalman_fitter_status::ERROR_INVERSION;
         }
 
-        // Update the bound track parameters
-        bound_params.set_vector(filtered_vec);
-        bound_params.set_covariance(filtered_cov);
+        if (std::abs(bound_params.qop()) == 0.f) {
+            return kalman_fitter_status::ERROR_QOP_ZERO;
+        }
 
         // Set backward chi2
         trk_state.backward_chi2() = getter::element(chi2, 0, 0);