diff --git a/kerchunk/combine.py b/kerchunk/combine.py
index eb891de1..b30b8707 100644
--- a/kerchunk/combine.py
+++ b/kerchunk/combine.py
@@ -304,7 +304,11 @@ def _get_value(self, index, z, var, fn=None):
         elif isinstance(selector, list):
             o = selector[index]
         elif isinstance(selector, re.Pattern):
-            o = selector.search(fn).groups()[0]
+            regex_groups_o = selector.search(fn).groups()
+            if len(regex_groups_o) == 0:
+                o = selector.search(fn).group()
+            else:
+                o = regex_groups_o[0]
         elif not isinstance(selector, str):
             # constant, should be int or float
             o = selector