diff --git a/scripts/qapi.py b/scripts/qapi.py
index 30f1483..9f98413 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -499,21 +499,6 @@ def check_type(expr_info, source, value, allow_array=False,
                                 'enum'])


-def check_member_clash(expr_info, base_name, data, source=""):
-    base = find_struct(base_name)
-    assert base
-    base_members = base['data']
-    for key in data.keys():
-        if key.startswith('*'):
-            key = key[1:]
-        if key in base_members or "*" + key in base_members:
-            raise QAPIExprError(expr_info,
-                                "Member name '%s'%s clashes with base '%s'"
-                                % (key, source, base_name))
-    if base.get('base'):
-        check_member_clash(expr_info, base['base'], data, source)
-
-
 def check_command(expr, expr_info):
     name = expr['command']

@@ -592,30 +577,18 @@ def check_union(expr, expr_info):
     for (key, value) in members.items():
         check_name(expr_info, "Member of union '%s'" % name, key)

-        # Each value must name a known type; furthermore, in flat unions,
-        # branches must be a struct with no overlapping member names
+        # Each value must name a known type
         check_type(expr_info, "Member '%s' of union '%s'" % (key, name),
                    value, allow_array=not base, allow_metas=allow_metas)
-        if base:
-            branch_struct = find_struct(value)
-            assert branch_struct
-            check_member_clash(expr_info, base, branch_struct['data'],
-                               " of branch '%s'" % key)

         # If the discriminator names an enum type, then all members
-        # of 'data' must also be members of the enum type, which in turn
-        # must not collide with the discriminator name.
+        # of 'data' must also be members of the enum type.
         if enum_define:
             if key not in enum_define['enum_values']:
                 raise QAPIExprError(expr_info,
                                     "Discriminator value '%s' is not found in "
                                     "enum '%s'" %
                                     (key, enum_define["enum_name"]))
-            if discriminator in enum_define['enum_values']:
-                raise QAPIExprError(expr_info,
-                                    "Discriminator name '%s' collides with "
-                                    "enum value in '%s'" %
-                                    (discriminator, enum_define["enum_name"]))

         # Otherwise, check for conflicts in the generated enum
         else:
@@ -690,8 +663,6 @@ def check_struct(expr, expr_info):
                allow_dict=True, allow_optional=True)
     check_type(expr_info, "'base' for struct '%s'" % name, expr.get('base'),
                allow_metas=['struct'])
-    if expr.get('base'):
-        check_member_clash(expr_info, expr['base'], expr['data'])


 def check_keys(expr_elem, meta, required, optional=[]):
@@ -1095,16 +1066,30 @@ class QAPISchemaObjectTypeVariants(object):
         assert isinstance(self.tag_member.type, QAPISchemaEnumType)
         for v in self.variants:
             vseen = dict(seen)
-            v.check(schema, info, self.tag_member.type, vseen)
+            v.check(schema, info, self.tag_member.type, vseen,
+                    bool(self.tag_name))


 class QAPISchemaObjectTypeVariant(QAPISchemaObjectTypeMember):
     def __init__(self, name, typ):
         QAPISchemaObjectTypeMember.__init__(self, name, typ, False)

-    def check(self, schema, info, tag_type, seen):
+    def check(self, schema, info, tag_type, seen, flat):
         QAPISchemaObjectTypeMember.check(self, schema, info, [], seen)
         assert self.name in tag_type.values
+        if flat:
+            # For flat unions, check that each QMP member does not
+            # collide with any non-variant members. No type can
+            # contain itself as a flat variant
+            self.type.check(schema)
+            assert not self.type.variants    # not implemented
+            for m in self.type.members:
+                if m.c_name() in seen:
+                    raise QAPIExprError(info,
+                                        "Member '%s' of branch '%s' collides "
+                                        "with %s"
+                                        % (m.name, self.name,
+                                           seen[m.c_name()].describe()))

     # This function exists to support ugly simple union special cases
     # TODO get rid of them, and drop the function
diff --git a/tests/qapi-schema/flat-union-clash-member.err b/tests/qapi-schema/flat-union-clash-member.err
index 2f0397a..57dd478 100644
--- a/tests/qapi-schema/flat-union-clash-member.err
+++ b/tests/qapi-schema/flat-union-clash-member.err
@@ -1 +1 @@
-tests/qapi-schema/flat-union-clash-member.json:11: Member name 'name' of branch 'value1' clashes with base 'Base'
+tests/qapi-schema/flat-union-clash-member.json:11: Member 'name' of branch 'value1' collides with 'name' (member of Base)
diff --git a/tests/qapi-schema/flat-union-clash-type.err b/tests/qapi-schema/flat-union-clash-type.err
index b44dd40..3f3248b 100644
--- a/tests/qapi-schema/flat-union-clash-type.err
+++ b/tests/qapi-schema/flat-union-clash-type.err
@@ -1 +1 @@
-tests/qapi-schema/flat-union-clash-type.json:11: Discriminator name 'type' collides with enum value in 'TestEnum'
+tests/qapi-schema/flat-union-clash-type.json:11: 'type' (branch of TestUnion) collides with 'type' (member of Base)
diff --git a/tests/qapi-schema/struct-base-clash-deep.err b/tests/qapi-schema/struct-base-clash-deep.err
index f7a25a3..e2d7943 100644
--- a/tests/qapi-schema/struct-base-clash-deep.err
+++ b/tests/qapi-schema/struct-base-clash-deep.err
@@ -1 +1 @@
-tests/qapi-schema/struct-base-clash-deep.json:10: Member name 'name' clashes with base 'Base'
+tests/qapi-schema/struct-base-clash-deep.json:10: 'name' (member of Sub) collides with 'name' (member of Base)
diff --git a/tests/qapi-schema/struct-base-clash.err b/tests/qapi-schema/struct-base-clash.err
index 3a9f66b..c52f33d 100644
--- a/tests/qapi-schema/struct-base-clash.err
+++ b/tests/qapi-schema/struct-base-clash.err
@@ -1 +1 @@
-tests/qapi-schema/struct-base-clash.json:5: Member name 'name' clashes with base 'Base'
+tests/qapi-schema/struct-base-clash.json:5: 'name' (member of Sub) collides with 'name' (member of Base)
