diff --git a/batdetect2/utils/detector_utils.py b/batdetect2/utils/detector_utils.py
index 1d92b26..c5dd4d0 100644
--- a/batdetect2/utils/detector_utils.py
+++ b/batdetect2/utils/detector_utils.py
@@ -731,7 +731,7 @@ def process_file(
         config["chunk_size"],
     ):
         # Run detection model on chunk
-        pred_nms, features, spec_np = _process_audio_array(
+        pred_nms, features, spec = _process_audio_array(
             audio,
             sampling_rate,
             model,
@@ -739,6 +739,9 @@ def process_file(
             device,
         )
 
+        # convert to numpy
+        spec_np = spec.detach().cpu().numpy()
+
         # add chunk time to start and end times
         pred_nms["start_times"] += chunk_time
         pred_nms["end_times"] += chunk_time
@@ -756,6 +759,7 @@ def process_file(
             cnn_feats.append(features[0])
 
         if config["spec_slices"]:
+            # FIX: This is not currently working. Returns empty slices
             spec_slices.extend(
                 feats.extract_spec_slices(spec_np, pred_nms, config)
             )
diff --git a/tests/test_api.py b/tests/test_api.py
index d20ebf4..942a1f1 100644
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -251,3 +251,14 @@ def test_postprocess_model_outputs():
     assert isinstance(features, np.ndarray)
     assert features.shape[0] == len(predictions)
     assert features.shape[1] == 32
+
+
+def test_process_file_with_spec_slices():
+    """Test process file returns spec slices."""
+    config = api.get_config(spec_slices=True)
+    results = api.process_file(TEST_DATA[0], config=config)
+    detections = results["pred_dict"]["annotation"]
+
+    assert "spec_slices" in results
+    assert isinstance(results["spec_slices"], list)
+    assert len(results["spec_slices"]) == len(detections)