diff --git a/ipykernel/kernelapp.py b/ipykernel/kernelapp.py
index 9628c7d5..723f5672 100644
--- a/ipykernel/kernelapp.py
+++ b/ipykernel/kernelapp.py
@@ -725,6 +725,8 @@ def start(self):
                 self.io_loop.start()
             except KeyboardInterrupt:
                 pass
+            finally:
+                self.io_loop.close()
 
 
 launch_new_instance = IPKernelApp.launch_instance