diff --git a/mbtrack2/tracking/emfields.py b/mbtrack2/tracking/emfields.py
index 3780ebbe9193e3ae7f3cbcd4cd147381f2eb4821..a451471c4f7e66c41cd4f431b66c7a73fb86f407 100644
--- a/mbtrack2/tracking/emfields.py
+++ b/mbtrack2/tracking/emfields.py
@@ -104,8 +104,8 @@ def efieldn_gauss_round(x, y, sig_x, sig_y):
     """
     r_squared = x*x + y*y
     sig_r = sig_x
-    amplitude = (1 - np.exp(-r_squared /
-                            (2*sig_r*sig_r))) / (2*pi*epsilon_0*r_squared)
+    amplitude = -np.expm1(-r_squared /
+                          (2*sig_r*sig_r)) / (2*pi*epsilon_0*r_squared)
     return x * amplitude, y * amplitude