diff --git a/hapi/metrics.py b/hapi/metrics.py
index 6fae7204e8ba8da32032e23f5688d3e5ba563c21..5064c4a97c958777523eabf71eadaa03e30a72b0 100644
--- a/hapi/metrics.py
+++ b/hapi/metrics.py
@@ -54,7 +54,7 @@ class Metric(object):
 
         Inputs of :code:`update` is the outputs of :code:`add_metric_op`, if
         :code:`add_metric_op` is not defined, the inputs of :code:`update` will
-        be a flatten argument of **output** of mode and **label** from data:
+        be flatten arguments of **output** of mode and **label** from data:
         :code:`update(output1, output2, ..., label1, label2,...)`
 
         see :code:`add_metric_op`