diff --git a/charon_vna/util.py b/charon_vna/util.py
index 249131a..a3fe0d2 100644
--- a/charon_vna/util.py
+++ b/charon_vna/util.py
@@ -47,7 +47,7 @@ def db20(v: npt.ArrayLike) -> npt.ArrayLike:
 
 
 def s2vswr(s: npt.ArrayLike) -> npt.ArrayLike:
-    return (1 + np.abs(s)) / (1 - np.abs(s))
+    return np.abs((1 + np.abs(s)) / (1 - np.abs(s)))
 
 
 def minmax(x):