diff --git a/fusilli/data.py b/fusilli/data.py
index ad833c6..2a2a505 100644
--- a/fusilli/data.py
+++ b/fusilli/data.py
@@ -225,16 +225,18 @@ def __init__(self, sources, img_downsample_dims=None):
         # read in the csv files and raise errors if they don't have the right columns
         # or if the index column is not named "ID"
         tab1_df = pd.read_csv(self.tabular1_source)
-        tab2_df = pd.read_csv(self.tabular2_source)
-
         if "ID" not in tab1_df.columns:
             raise ValueError("The CSV must have an index column named 'ID'.")
         if "prediction_label" not in tab1_df.columns:
             raise ValueError("The CSV must have a label column named 'prediction_label'.")
-        if "ID" not in tab2_df.columns:
-            raise ValueError("The CSV must have an index column named 'ID'.")
-        if "prediction_label" not in tab2_df.columns:
-            raise ValueError("The CSV must have a label column named 'prediction_label'.")
+
+        # if tabular2_source exists, check it has the right columns
+        if self.tabular2_source != "":
+            tab2_df = pd.read_csv(self.tabular2_source)
+            if "ID" not in tab2_df.columns:
+                raise ValueError("The CSV must have an index column named 'ID'.")
+            if "prediction_label" not in tab2_df.columns:
+                raise ValueError("The CSV must have a label column named 'prediction_label'.")
 
     def load_tabular1(self):
         """