diff --git a/monai/engines/evaluator.py b/monai/engines/evaluator.py
index e1fecb745d..71b5069705 100644
--- a/monai/engines/evaluator.py
+++ b/monai/engines/evaluator.py
@@ -188,8 +188,7 @@ def __init__(
             val_handlers=val_handlers,
             amp=amp,
             mode=mode,
-            # add the iteration events
-            event_names=[IterationEvents] if event_names is None else event_names + [IterationEvents],
+            event_names=event_names,
             event_to_attr=event_to_attr,
         )
 
@@ -306,8 +305,7 @@ def __init__(
             val_handlers=val_handlers,
             amp=amp,
             mode=mode,
-            # add the iteration events
-            event_names=[IterationEvents] if event_names is None else event_names + [IterationEvents],
+            event_names=event_names,
             event_to_attr=event_to_attr,
         )
 
diff --git a/monai/engines/trainer.py b/monai/engines/trainer.py
index e9e31a1b16..d017bce70d 100644
--- a/monai/engines/trainer.py
+++ b/monai/engines/trainer.py
@@ -120,8 +120,7 @@ def __init__(
             additional_metrics=additional_metrics,
             handlers=train_handlers,
             amp=amp,
-            # add the iteration events
-            event_names=[IterationEvents] if event_names is None else event_names + [IterationEvents],
+            event_names=event_names,
             event_to_attr=event_to_attr,
         )
 
diff --git a/monai/engines/workflow.py b/monai/engines/workflow.py
index abc4ca269e..9e1516937f 100644
--- a/monai/engines/workflow.py
+++ b/monai/engines/workflow.py
@@ -137,16 +137,14 @@ def set_sampler_epoch(engine: Engine):
         self.prepare_batch = prepare_batch
         self.amp = amp
 
-        if event_names is not None:
-            if not isinstance(event_names, list):
+        event_names = [IterationEvents] if event_names is None else event_names + [IterationEvents]
+        for name in event_names:
+            if isinstance(name, str):
+                self.register_events(name, event_to_attr=event_to_attr)
+            elif issubclass(name, EventEnum):
+                self.register_events(*name, event_to_attr=event_to_attr)
+            else:
                 raise ValueError("event_names must be a list or string or EventEnum.")
-            for name in event_names:
-                if isinstance(name, str):
-                    self.register_events(name, event_to_attr=event_to_attr)
-                elif issubclass(name, EventEnum):
-                    self.register_events(*name, event_to_attr=event_to_attr)
-                else:
-                    raise ValueError("event_names must be a list or string or EventEnum.")
 
         if post_transform is not None:
             self._register_post_transforms(post_transform)