diff --git a/utils.py b/utils.py
index f9e0d6a..fdab317 100644
--- a/utils.py
+++ b/utils.py
@@ -97,7 +97,7 @@ def random_shadow(image):
     # as x2 == x1 causes zero-division problem, we'll write it in the below form:
     # (ym-y1)*(x2-x1) - (y2-y1)*(xm-x1) > 0
     mask = np.zeros_like(image[:, :, 1])
-    mask[(ym - y1) * (x2 - x1) - (y2 - y1) * (xm - x1) > 0] = 1
+    mask[np.where((ym - y1) * (x2 - x1) - (y2 - y1) * (xm - x1) > 0)] = 1
 
     # choose which side should have shadow and adjust saturation
     cond = mask == np.random.randint(2)