diff --git a/core/classes/algebra/algebra-tests.factor b/core/classes/algebra/algebra-tests.factor
index 78da6ee9b3..444cf50e58 100755
--- a/core/classes/algebra/algebra-tests.factor
+++ b/core/classes/algebra/algebra-tests.factor
@@ -3,7 +3,7 @@ kernel math namespaces parser prettyprint sequences strings
 tools.test vectors words quotations classes classes.algebra
 classes.private classes.union classes.mixin classes.predicate
 vectors definitions source-files compiler.units growable
-random inference effects kernel.private sbufs math.order
+random inference effects kernel.private sbufs math.order
 classes.tuple ;
 IN: classes.algebra.tests
 
@@ -288,6 +288,8 @@ INTERSECTION: generic-class generic class ;
     generic-class flatten-class
 ] unit-test
 
+[ \ + flatten-class ] must-fail
+
 INTERSECTION: empty-intersection ;
 
 [ t ] [ object empty-intersection class<= ] unit-test
diff --git a/core/classes/algebra/algebra.factor b/core/classes/algebra/algebra.factor
index 9dbe72d9cb..1076901678 100755
--- a/core/classes/algebra/algebra.factor
+++ b/core/classes/algebra/algebra.factor
@@ -207,9 +207,6 @@ GENERIC: (flatten-class) ( class -- )
 M: anonymous-union (flatten-class)
     members>> [ (flatten-class) ] each ;
 
-M: word (flatten-class)
-    normalize-class (flatten-class) ;
-
 : flatten-class ( class -- assoc )
     [ (flatten-class) ] H{ } make-assoc ;
 
diff --git a/core/classes/intersection/intersection.factor b/core/classes/intersection/intersection.factor
index 5df580d82f..bb7e0adc62 100644
--- a/core/classes/intersection/intersection.factor
+++ b/core/classes/intersection/intersection.factor
@@ -31,3 +31,6 @@ M: intersection-class rank-class drop 2 ;
 
 M: intersection-class instance?
     "participants" word-prop [ instance? ] with all? ;
+
+M: intersection-class (flatten-class)
+    participants <anonymous-intersection> (flatten-class) ;
diff --git a/core/classes/union/union.factor b/core/classes/union/union.factor
index e3deb25e7a..fbb1925363 100755
--- a/core/classes/union/union.factor
+++ b/core/classes/union/union.factor
@@ -32,3 +32,6 @@ M: union-class rank-class drop 2 ;
 
 M: union-class instance?
     "members" word-prop [ instance? ] with contains? ;
+
+M: union-class (flatten-class)
+    members <anonymous-union> (flatten-class) ;