diff --git a/src/cpl_query/base/queryable_abc.py b/src/cpl_query/base/queryable_abc.py
index b14f63b2..be201073 100644
--- a/src/cpl_query/base/queryable_abc.py
+++ b/src/cpl_query/base/queryable_abc.py
@@ -221,7 +221,7 @@ class QueryableABC(Sequence):
 
         for v in self:
             value = _func(v)
-            if v not in groups:
+            if value not in groups:
                 groups[value] = []
 
             groups[value].append(v)