diff --git a/kubespawner/spawner.py b/kubespawner/spawner.py
index 19121724..e6645f1f 100644
--- a/kubespawner/spawner.py
+++ b/kubespawner/spawner.py
@@ -781,7 +781,7 @@ def _deprecated_changed(self, change):
 
     @validate('image_pull_secrets')
     def _validate_image_pull_secrets(self, proposal):
-        if type(proposal['value']) == str:
+        if isinstance(proposal['value'], str):
             warnings.warn(
                 """Passing KubeSpawner.image_pull_secrets string values is
                 deprecated since KubeSpawner 0.14.0. The recommended