diff --git a/simulate/simulate.cc b/simulate/simulate.cc
index d6a5f80e..a266c57a 100644
--- a/simulate/simulate.cc
+++ b/simulate/simulate.cc
@@ -299,7 +299,7 @@ void UpdateProfiler(mj::Simulate* sim, const mjModel* m, const mjData* d) {
   memset(sim->figcost.linepnt, 0, mjMAXLINE*sizeof(int));
 
   // number of islands that have diagnostics
-  int nisland = mjMAX(1, mjMIN(d->nisland, mjNISLAND));
+  int nisland = d->nefc ? mjMAX(1, mjMIN(d->nisland, mjNISLAND)) : 0;
 
   // iterate over islands
   for (int k=0; k < nisland; k++) {
@@ -403,9 +403,10 @@ void UpdateProfiler(mj::Simulate* sim, const mjModel* m, const mjData* d) {
   mjtNum sqrt_nnz = 0;
   int solver_niter = 0;
   for (int island=0; island < nisland; island++) {
-    sqrt_nnz += mju_sqrt(d->solver_nnz[island]);
+    sqrt_nnz += d->solver_nnz[island];
     solver_niter += d->solver_niter[island];
   }
+  sqrt_nnz = mju_sqrt(sqrt_nnz);
 
   // get sizes: nv, nbody, nefc, sqrt(nnz), ncont, iter
   float sdata[6] = {
diff --git a/src/experimental/studio/app.cc b/src/experimental/studio/app.cc
index a214a092..5b3ff75a 100644
--- a/src/experimental/studio/app.cc
+++ b/src/experimental/studio/app.cc
@@ -634,14 +634,15 @@ void App::UpdateProfilerData() {
   cpu_other_.erase(cpu_other_.begin());
   cpu_other_.push_back(other);
 
-  // Dimensions.
+  // Solver diagnostics.
   mjtNum sqrt_nnz = 0;
   int solver_niter = 0;
-  const int nisland = mjMAX(1, mjMIN(Data()->nisland, mjNISLAND));
-  for (int island = 0; island < nisland; island++) {
-    sqrt_nnz += mju_sqrt(Data()->solver_nnz[island]);
+  const int nisland = Data()->nefc ? mjMAX(1, mjMIN(Data()->nisland, mjNISLAND)) : 0;
+  for (int island=0; island < nisland; island++) {
+    sqrt_nnz += Data()->solver_nnz[island];
     solver_niter += Data()->solver_niter[island];
   }
+  sqrt_nnz = mju_sqrt(sqrt_nnz);
 
   dim_dof_.erase(dim_dof_.begin());
   dim_dof_.push_back(Model()->nv);