diff --git a/mmengine/runner/loops.py b/mmengine/runner/loops.py
index 5a678db7b9..822756ef25 100644
--- a/mmengine/runner/loops.py
+++ b/mmengine/runner/loops.py
@@ -403,7 +403,8 @@ def run_iter(self, idx, data_batch: Sequence[dict]):
         with autocast(enabled=self.fp16):
             outputs = self.runner.model.val_step(data_batch)
 
-        outputs, self.val_loss = _update_losses(outputs, self.val_loss)
+        if isinstance(outputs, list):
+            outputs, self.val_loss = _update_losses(outputs, self.val_loss)
 
         self.evaluator.process(data_samples=outputs, data_batch=data_batch)
         self.runner.call_hook(
@@ -486,7 +487,8 @@ def run_iter(self, idx, data_batch: Sequence[dict]) -> None:
         with autocast(enabled=self.fp16):
             outputs = self.runner.model.test_step(data_batch)
 
-        outputs, self.test_loss = _update_losses(outputs, self.test_loss)
+        if isinstance(outputs, list):
+            outputs, self.test_loss = _update_losses(outputs, self.test_loss)
 
         self.evaluator.process(data_samples=outputs, data_batch=data_batch)
         self.runner.call_hook(