diff --git a/src/hdf5_lib.py b/src/hdf5_lib.py
index 7c498a1..cab8554 100644
--- a/src/hdf5_lib.py
+++ b/src/hdf5_lib.py
@@ -495,7 +495,9 @@ def save_processed_dataframe_to_hdf5(df, annotator, src_hdf5_path, script_date,
     """
     # Convert datetime columns to string
     datetime_cols = df.select_dtypes(include=['datetime64']).columns
-    df[datetime_cols] = df[datetime_cols].apply(str)
+
+    if list(datetime_cols):
+        df[datetime_cols] = df[datetime_cols].map(str)
 
     # Convert dataframe to structured array
     icad_data_table = utils.dataframe_to_np_structured_array(df)