diff --git a/popt/loop/optimize.py b/popt/loop/optimize.py
index e577c11..30074da 100644
--- a/popt/loop/optimize.py
+++ b/popt/loop/optimize.py
@@ -206,7 +206,7 @@ def run_loop(self):
                     logger.info(f'       -----> EPF-EnOpt: {self.epf_iteration}, {r} (outer iteration, penalty factor)')  # print epf info
                 else:
                     logger.info(f'       -----> EPF-EnOpt: converged, no variables changed more than {conv_crit*100} %')  # print epf info
-                    final_obj_no_penalty = str(round(self.fun(self.mean_state),4))
+                    final_obj_no_penalty = str(round(float(self.fun(self.mean_state)),4))
                     logger.info(f'       -----> EPF-EnOpt: objective value without penalty = {final_obj_no_penalty}') # print epf info
 
     def save(self):