diff --git a/mist/analyze_data/analyze.py b/mist/analyze_data/analyze.py
index 8d1c5fb..f3afaf3 100755
--- a/mist/analyze_data/analyze.py
+++ b/mist/analyze_data/analyze.py
@@ -112,9 +112,13 @@ def compute_class_weights(self):
         """Compute class weights on original data."""
 
         # Either compute class weights or use user provided weights.
-        # Check that number of class weights matches the number of labels.
+        # Check that number of class weights matches the number of labels if
+        # provided.
         n_labels = len(self.dataset_information["labels"])
-        if len(self.mist_arguments.class_weights) != n_labels:
+        if (
+            self.mist_arguments.class_weights and
+            len(self.mist_arguments.class_weights) != n_labels
+        ):
             raise ValueError(
                 "Number of class weights must match number of labels."
             )
@@ -185,7 +189,7 @@ def get_target_spacing(self):
                 # to make sure that all of the axes in the spacings match up.
                 # We load the masks because they are smaller and faster to load.
                 mask = ants.image_read(patient["mask"])
-                mask = mask.reorient_image2(mask, "RAI")
+                mask = ants.reorient_image2(mask, "RAI")
                 mask.set_direction(
                     analyzer_constants.AnalyzeConstants.RAI_ANTS_DIRECTION
                 )