diff --git a/tracking/element.py b/tracking/element.py
index 6f23f7d1a39dbbc447c39140310a7a1a810fb1c7..34fdc76fb0f49d39c9cbfe24bd65e719cb95e6b1 100644
--- a/tracking/element.py
+++ b/tracking/element.py
@@ -135,7 +135,7 @@ class SynchrotronRadiation(Element):
         if (self.switch[2] == True):
             rand = np.random.normal(size=len(bunch))
             bunch["yp"] = ((1 - 2*self.ring.T0/self.ring.tau[1])*bunch["yp"] +
-                 2*self.ring.sigma()[1]*(self.ring.T0/self.ring.tau[1])**0.5*rand)
+                 2*self.ring.sigma()[3]*(self.ring.T0/self.ring.tau[1])**0.5*rand)
         
 class TransverseMap(Element):
     """