diff --git a/nifty/minimization/quasi_newton_minimizer.py b/nifty/minimization/quasi_newton_minimizer.py
index 96915424953fcca0004f9ddb8c4b3ba58080fdc2..d413c686596ed54013fc10c7d4707807e1053b50 100644
--- a/nifty/minimization/quasi_newton_minimizer.py
+++ b/nifty/minimization/quasi_newton_minimizer.py
@@ -56,7 +56,7 @@ class QuasiNewtonMinimizer(object, Loggable):
 
         """
 
-        x = x0
+        x = x0.copy()
         self.line_searcher.set_functions(f=f, fprime=fprime, f_args=f_args)
 
         convergence = 0