diff --git a/python/backends/trueskillWrapper.py b/python/backends/trueskillWrapper.py
index 4b60610..711bca3 100644
--- a/python/backends/trueskillWrapper.py
+++ b/python/backends/trueskillWrapper.py
@@ -98,7 +98,7 @@ def predictOutcome(teamA, teamB):
     # than a random point from  normDistB is normA - normB and then the
     # "1 - Cumulative Distribution Function" (cdf) aka the "Survival Function" (sf)
     # of the resulting distribution being greater than zero
-    prob = scipy.stats.norm(loc=muTeamB-muTeamA, scale=math.sqrt(sigmaTeamB**2-sigmaTeamA**2)).sf(0)
+    prob = scipy.stats.norm(loc=muTeamB-muTeamA, scale=math.sqrt(abs(sigmaTeamB**2-sigmaTeamA**2))).sf(0)
     if prob >= 0.5:
         return (0, prob)
     elif prob < 0.5: