diff --git a/matlab/optimization/dynare_minimize_objective.m b/matlab/optimization/dynare_minimize_objective.m
index 13d1eae6e0d5c80b2699ef5da3eb819e7e192d22..97b27af9b98340a9a3fdc51d9082d9f029117bd1 100644
--- a/matlab/optimization/dynare_minimize_objective.m
+++ b/matlab/optimization/dynare_minimize_objective.m
@@ -51,7 +51,7 @@ if isempty(bounds)
 end
 
 if isempty(parameter_names)
-    parameter_names=[repmat('parameter ',n_params,1),num2str((1:n_params)')];
+    parameter_names=cellstr([repmat('parameter ',n_params,1),num2str((1:n_params)')]);
 end
 
 %% initialize function outputs