diff -up src/sage/interfaces/ecm.py.orig src/sage/interfaces/ecm.py --- src/sage/interfaces/ecm.py.orig 2018-12-22 16:37:08.000000000 -0700 +++ src/sage/interfaces/ecm.py 2019-01-15 10:26:31.060040736 -0700 @@ -256,7 +256,7 @@ class ECM(SageObject): """ print("Enter numbers to run ECM on them.") print("Press control-C to exit.") - os.system(self._cmd) + os.system(' '.join(self._cmd)) # Recommended settings from # http://www.mersennewiki.org/index.php/Elliptic_Curve_Method