diff --git a/matlab/optimization/dynare_minimize_objective.m b/matlab/optimization/dynare_minimize_objective.m
index 59ea287f1c3109aed3b5525613ccd47afe36a370..a7e6a83f5dc7f4158d5dd5e5e0e896d2d97fd23a 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