diff --git a/goratings/math/glicko2.py b/goratings/math/glicko2.py
index b28f215..ecbd3e3 100644
--- a/goratings/math/glicko2.py
+++ b/goratings/math/glicko2.py
@@ -133,7 +133,7 @@ def f(x: float) -> float:
     while abs(B - A) > EPSILON and safety > 0:
         C = A + (A - B) * fA / (fB - fA)
         fC = f(C)
-        if fC * fB < 0:
+        if fC * fB <= 0:
             A = B
             fA = fB
         else: