diff --git a/nbconvert/preprocessors/execute.py b/nbconvert/preprocessors/execute.py
index 45587d345..284c76945 100644
--- a/nbconvert/preprocessors/execute.py
+++ b/nbconvert/preprocessors/execute.py
@@ -480,7 +480,7 @@ def run_cell(self, cell, cell_index=0):
                 continue
             elif msg_type.startswith('comm'):
                 self.handle_comm_msg(outs, msg, cell_index)
-                self.widget_state[content['comm_id']] = content['data']['state']
+                self.widget_state.setdefault(content['comm_id'], {}).update(content['data']['state'])
                 continue
 
             display_id = None