diff --git a/topaz/utils/data/train_test_split_micrographs.py b/topaz/utils/data/train_test_split_micrographs.py
index fa9f7de..5a5a1f4 100644
--- a/topaz/utils/data/train_test_split_micrographs.py
+++ b/topaz/utils/data/train_test_split_micrographs.py
@@ -40,8 +40,8 @@ def train_test_split_micrographs(seed, n, path, format, image_dir, file_ext):
         image_names_train.append(image_names[j])
         groups_train.append(groups[j])
     
-    targets_train = pd.concat(groups_train, 0)
-    targets_test = pd.concat(groups_test, 0)
+    targets_train = pd.concat(groups_train, axis=0)
+    targets_test = pd.concat(groups_test, axis=0)
 
 
     ## if the image-dir is specified, make the image list files