diff --git a/matlab/model_diagnostics.m b/matlab/model_diagnostics.m
index a01947939e9a5197ca3395461b3b713863410a41..6a1cd8a2445adc48487a763c2c810b2c83d9f0c0 100644
--- a/matlab/model_diagnostics.m
+++ b/matlab/model_diagnostics.m
@@ -160,6 +160,7 @@ for b=1:nb
                                     'evaluate', 'static', 'block_decomposed', ['block=' ...
                                 int2str(b)]);
         end
+        n_vars_jacob=size(jacob,2);
     else
         if options_.block
             T = NaN(M_.block_structure_stat.tmp_nbr, 1);