diff --git a/tidy3d/components/medium.py b/tidy3d/components/medium.py
index e2f4a69005..6150078ec7 100644
--- a/tidy3d/components/medium.py
+++ b/tidy3d/components/medium.py
@@ -163,7 +163,7 @@ def eps_sigma_to_eps_complex(eps_real: float, sigma: float, freq: float) -> comp
         complex
             Complex-valued relative permittivity.
         """
-        if not freq:
+        if freq is None:
             return eps_real
         omega = 2 * np.pi * freq
         return eps_real + 1j * sigma / omega