diff --git a/avalanche/evaluation/metrics/detection.py b/avalanche/evaluation/metrics/detection.py
index 2e01df060..513dc53d6 100644
--- a/avalanche/evaluation/metrics/detection.py
+++ b/avalanche/evaluation/metrics/detection.py
@@ -19,6 +19,7 @@
 )
 
 from avalanche.benchmarks.utils.data import AvalancheDataset
+from avalanche.benchmarks.utils.data import _FlatDataWithTransform
 
 try:
     from lvis import LVIS
@@ -470,12 +471,12 @@ def get_detection_api_from_dataset(
         recursion_result = get_detection_api_from_dataset(
             dataset.dataset, supported_types, none_if_not_found=True
         )
-    elif isinstance(dataset, AvalancheDataset) and len(dataset._datasets) == 1:
+    elif isinstance(dataset, (AvalancheDataset, _FlatDataWithTransform)) and len(dataset._datasets) == 1:
         recursion_result = get_detection_api_from_dataset(
             dataset._datasets[0], supported_types, none_if_not_found=True
         )
-    elif isinstance(dataset, (AvalancheDataset, ConcatDataset)):
-        if isinstance(dataset, AvalancheDataset):
+    elif isinstance(dataset, (AvalancheDataset, ConcatDataset, _FlatDataWithTransform)):
+        if isinstance(dataset, (AvalancheDataset, _FlatDataWithTransform)):
             datasets_list = dataset._datasets
         else:
             datasets_list = dataset.datasets