diff --git a/nbconvert/preprocessors/execute.py b/nbconvert/preprocessors/execute.py
index d764bd744..1bf771c86 100644
--- a/nbconvert/preprocessors/execute.py
+++ b/nbconvert/preprocessors/execute.py
@@ -281,26 +281,29 @@ def start_new_kernel(startup_timeout=60, kernel_name='python', **kwargs):
         finally:
             self.kc.stop_channels()
             self.km.shutdown_kernel(now=self.shutdown_kernel == 'immediate')
-            if self.widget_state:
-                self.nb.metadata.widgets = {
-                    'application/vnd.jupyter.widget-state+json': {
-                        'state': {
-                            model_id: _serialize_widget_state(state)
-                            for model_id, state in self.widget_state.items() if '_model_name' in state
-                        },
-                        'version_major': 2,
-                        'version_minor': 0,
-                    }
-                }
-                for key, widget in self.nb.metadata.widgets['application/vnd.jupyter.widget-state+json']['state'].items():
-                    buffers = self.widget_buffers.get(key)
-                    if buffers:
-                        widget['buffers'] = buffers
+            self.set_widgets_metadata()
 
         delattr(self, 'nb')
 
         return nb, resources
 
+    def set_widgets_metadata(self):
+        if self.widget_state:
+            self.nb.metadata.widgets = {
+                'application/vnd.jupyter.widget-state+json': {
+                    'state': {
+                        model_id: _serialize_widget_state(state)
+                        for model_id, state in self.widget_state.items() if '_model_name' in state
+                    },
+                    'version_major': 2,
+                    'version_minor': 0,
+                }
+            }
+            for key, widget in self.nb.metadata.widgets['application/vnd.jupyter.widget-state+json']['state'].items():
+                buffers = self.widget_buffers.get(key)
+                if buffers:
+                    widget['buffers'] = buffers
+
     def preprocess_cell(self, cell, resources, cell_index):
         """
         Executes a single code cell. See base.py for details.
diff --git a/setup.py b/setup.py
index 39af9dece..5aec4f312 100644
--- a/setup.py
+++ b/setup.py
@@ -199,7 +199,7 @@ def run(self):
 ]
 
 extra_requirements = {
-    'test': ['pytest', 'pytest-cov', 'ipykernel', 'jupyter_client>=4.2', 'ipywidgets'],
+    'test': ['pytest', 'pytest-cov', 'ipykernel', 'jupyter_client>=4.2', 'ipywidgets>=7'],
     'serve': ['tornado>=4.0'],
     'execute': ['jupyter_client>=4.2'],
 }