diff --git a/tensorboard/plugins/custom_scalar/custom_scalars_plugin.py b/tensorboard/plugins/custom_scalar/custom_scalars_plugin.py
index f3e302ff21f..84fa48d14bb 100644
--- a/tensorboard/plugins/custom_scalar/custom_scalars_plugin.py
+++ b/tensorboard/plugins/custom_scalar/custom_scalars_plugin.py
@@ -275,8 +275,11 @@ def layout_impl(self):
         for category in layout_proto.category:
           if category.title in title_to_category:
             # A category with this name has been seen before. Do not create a
-            # new one. Merge their charts.
-            title_to_category[category.title].chart.extend(category.chart)
+            # new one. Merge their charts, skipping any duplicates.
+            title_to_category[category.title].chart.extend([
+                c for c in category.chart
+                if c not in title_to_category[category.title].chart
+            ])
           else:
             # This category has not been seen before.
             merged_layout.category.add().MergeFrom(category)
diff --git a/tensorboard/plugins/custom_scalar/custom_scalars_plugin_test.py b/tensorboard/plugins/custom_scalar/custom_scalars_plugin_test.py
index b644d063c58..f4a20780523 100644
--- a/tensorboard/plugins/custom_scalar/custom_scalars_plugin_test.py
+++ b/tensorboard/plugins/custom_scalar/custom_scalars_plugin_test.py
@@ -78,7 +78,7 @@ def __init__(self, *args, **kwargs):
                 ]
             ),
             # A category with this name is also present in a layout for a
-            # different run (the logdir run)
+            # different run (the logdir run) and also contains a duplicate chart
             layout_pb2.Category(
                 title='cross entropy',
                 chart=[
@@ -92,6 +92,11 @@ def __init__(self, *args, **kwargs):
                                     upper='cross entropy upper'),
                             ],
                         )),
+                    layout_pb2.Chart(
+                        title='cross entropy',
+                        multiline=layout_pb2.MultilineChartContent(
+                            tag=[r'cross entropy'],
+                        )),
                 ]
             ),
         ]