diff --git a/src/engine/engine_vis_interact.c b/src/engine/engine_vis_interact.c
index 2e400e56..4ea29d55 100644
--- a/src/engine/engine_vis_interact.c
+++ b/src/engine/engine_vis_interact.c
@@ -556,8 +556,7 @@ void mjv_initPerturb(const mjModel* m, mjData* d, const mjvScene* scn, mjvPertur
 
   // compute average spatial inertia at selection point
   for (int i=0; i < nv; i++) {
-    int diag = d->M_rowadr[i] + d->M_rownnz[i] - 1;
-    sqrtInvD[i] = 1 / mju_sqrt(d->qLD[diag]);
+    sqrtInvD[i] = mju_sqrt(d->qLDiagInv[i]);
   }
   mj_jac(m, d, jac, NULL, selpos, sel);
   mj_solveM2(m, d, jacM2, jac, sqrtInvD, 3);