diff --git a/utils/utils.py b/utils/utils.py
index f7b80187..fe143fdb 100755
--- a/utils/utils.py
+++ b/utils/utils.py
@@ -449,8 +449,9 @@ def build_targets(model, targets):
         # Class
         tcls.append(c)
         if c.shape[0]:  # if any targets
-            assert c.max() <= model.nc, 'Model accepts %g classes labeled from 0-%g, however you supplied a label %g. \
-                See https://github.com/ultralytics/yolov3/wiki/Train-Custom-Data' % (model.nc, model.nc - 1, c.max())
+            assert c.max() < model.nc, 'Model accepts %g classes labeled from 0-%g, however you labelled a class %g. ' \
+                                       'See https://github.com/ultralytics/yolov3/wiki/Train-Custom-Data' % (
+                                           model.nc, model.nc - 1, c.max())
 
     return tcls, tbox, indices, av