Index: wflow/stats.py
===================================================================
diff -u -rc427e9b948a7fbad40a1c828b68355cb277dc5e0 -ra9498adee6baab0a0abaa331041be8948510167b
--- wflow/stats.py	(.../stats.py)	(revision c427e9b948a7fbad40a1c828b68355cb277dc5e0)
+++ wflow/stats.py	(.../stats.py)	(revision a9498adee6baab0a0abaa331041be8948510167b)
@@ -486,7 +486,9 @@
             Bvalues[i] != NoData and not np.isnan(Avalues[i])
         ):
             if Avalues[i] != Bvalues[i]:
-                curr_sign = (Avalues[i] - Bvalues[i]) / math.fabs(Avalues[i] - Bvalues[i])
+                curr_sign = (Avalues[i] - Bvalues[i]) / math.fabs(
+                    Avalues[i] - Bvalues[i]
+                )
             else:
                 curr_sign = sign
             if curr_sign != sign: