diff --git a/sarracenia/config.py b/sarracenia/config.py
index 78a2a4179..9091db9e1 100755
--- a/sarracenia/config.py
+++ b/sarracenia/config.py
@@ -891,7 +891,12 @@ def _varsub(self, word):
     def _build_mask(self, option, arguments):
         """ return new entry to be appended to list of masks
        """
-        regex = re.compile(arguments[0])
+        try:
+            regex = re.compile(arguments[0])
+        except:
+            logger.critical( f"invalid regular expression: {arguments[0]}, ignored." )
+            return None
+
         if len(arguments) > 1:
             fn = arguments[1]
         else: