diff --git a/CollectiveEffect/instabilities.py b/CollectiveEffect/instabilities.py
index 34bd52310f4f985cf8e8d321716c1193e0137bf8..ec2ffb48327a0646150f1d8f402c78c81a4bc5d9 100644
--- a/CollectiveEffect/instabilities.py
+++ b/CollectiveEffect/instabilities.py
@@ -37,7 +37,7 @@ def MBI_threshold(ring, sigma, R, b):
     Ia = 4*pi*epsilon_0*m_e*c**3/e # Alfven current
     chi = sigma*(R/b**3)**(1/2) # Shielding paramter
     xi = 0.5 + 0.34*chi
-    N = (ring.L0 * Ia * ring.ac * ring.gamma * ring.sigma_delta**2 * xi *
+    N = (ring.L * Ia * ring.ac * ring.gamma * ring.sigma_delta**2 * xi *
         sigma**(1/3) / ( c * e * R**(1/3) ))
     I = N*e/ring.T0