diff --git a/xlst_2_csv.py b/xlst_2_csv.py
index e1cfc9d1d..11c7bd499 100755
--- a/xlst_2_csv.py
+++ b/xlst_2_csv.py
@@ -24,10 +24,10 @@ def export_to_csv(input_file, output_file, columns, filters, sort_orders):
     df = df.sort_values(by=sort_columns, ascending=sort_ascending)
 
     # Drop filter-only columns that begin with an underscore
-    pattern = re.compile("^_[a-z]+$")
+    pattern = re.compile("^_[a-zA-Z]+$")
     for c in columns:
         if pattern.match(c):
-            df.pop(c) 
+            df.pop(c)
 
     # Export to CSV
     df.to_csv(output_file, index=False)