diff --git a/collective_effects/resistive_wall.py b/collective_effects/resistive_wall.py
index dc4c4bab312be03ee2bef1b8b90b9dc1ef81269d..eb5b1982360eab97fe3fa3749512bde1ed886514 100644
--- a/collective_effects/resistive_wall.py
+++ b/collective_effects/resistive_wall.py
@@ -147,7 +147,7 @@ class CircularResistiveWall(WakeField):
                                       np.cos( np.sqrt(3) * t / self.t0 )  
                                       - np.sqrt(2) / np.pi * val )
         else:
-            wl = (-1/(4*np.pi * self.radius) 
+            wl = (1/(4*np.pi * self.radius) 
                   * np.sqrt(Z0 * self.rho / (c * np.pi) ) 
                   / time**(3/2) ) * self.length
             ind = np.isnan(wl)