diff --git a/CHANGES.rst b/CHANGES.rst
index a114bded..f60b13b3 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -7,6 +7,10 @@ Changelog
 - Fix case where index value is changed to None after previously being indexed.
   (`#100 <https://github.com/zopefoundation/Products.ZCatalog/issues/100>`_)
 
+- Fix case where multiple indexes with similar name seperated by ``_`` were interpreted as options.
+  Fixes #78.
+  [thet]
+
 
 5.1 (2020-04-20)
 ----------------
diff --git a/src/Products/ZCatalog/query.py b/src/Products/ZCatalog/query.py
index 87a7309c..e18836dd 100644
--- a/src/Products/ZCatalog/query.py
+++ b/src/Products/ZCatalog/query.py
@@ -89,8 +89,8 @@ def __init__(self, request, iid, options=(), operators=('or', 'and'),
             for field in request.keys():
                 if field.startswith(iid + '_'):
                     iid_tmp, op = field.split('_')
-
-                    self.set(op, request[field])
+                    if op in self.options:
+                        self.set(op, request[field])
 
         self.keys = keys
         not_value = getattr(self, 'not', None)