Fix label names.
diff --git a/Doc/reference/expressions.rst b/Doc/reference/expressions.rst
index b3372a5..a7c66d3 100644
--- a/Doc/reference/expressions.rst
+++ b/Doc/reference/expressions.rst
@@ -1048,9 +1048,9 @@
 
 .. _comparisons:
 .. _is:
-.. _isnot:
+.. _is not:
 .. _in:
-.. _notin:
+.. _not in:
 
 Comparisons
 ===========