diff --git a/scripts/qapi.py b/scripts/qapi.py
index 38121c5..7c76442 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -329,6 +329,8 @@ class QAPISchemaParser(object):


 def find_base_members(base):
+    if isinstance(base, dict):
+        return base
     base_struct_define = find_struct(base)
     if not base_struct_define:
         return None
@@ -562,9 +564,9 @@ def check_union(expr, expr_info):

     # Else, it's a flat union.
     else:
-        # The object must have a string member 'base'.
+        # The object must have a string or dictionary 'base'.
         check_type(expr_info, "'base' for union '%s'" % name,
-                   base, allow_metas=['struct'])
+                   base, allow_dict=True, allow_metas=['struct'])
         if not base:
             raise QAPIExprError(expr_info,
                                 "Flat union '%s' must have a base"
@@ -1039,6 +1041,8 @@ class QAPISchemaMember(object):
             owner = owner[5:]
             if owner.endswith('-arg'):
                 return '(parameter of %s)' % owner[:-4]
+            elif owner.endswith('-base'):
+                return '(base of %s)' % owner[:-5]
             else:
                 assert owner.endswith('-wrapper')
                 # Unreachable and not implemented
@@ -1323,6 +1327,9 @@ class QAPISchema(object):
         base = expr.get('base')
         tag_name = expr.get('discriminator')
         tag_member = None
+        if isinstance(base, dict):
+            base = (self._make_implicit_object_type(
+                    name, info, 'base', self._make_members(base, info)))
         if tag_name:
             variants = [self._make_variant(key, value)
                         for (key, value) in data.iteritems()]
diff --git a/scripts/qapi-types.py b/scripts/qapi-types.py
index 1f090e6..161443e 100644
--- a/scripts/qapi-types.py
+++ b/scripts/qapi-types.py
@@ -72,13 +72,15 @@ struct %(c_name)s {
 ''',
                  c_name=c_name(name))

-    if base:
-        ret += mcgen('''
+    if base and not base.is_empty():
+        if not base.is_implicit():
+            ret += mcgen('''
     /* Members inherited from %(c_name)s: */
 ''',
-                     c_name=base.c_name())
+                         c_name=base.c_name())
         ret += gen_struct_members(base.members)
-        ret += mcgen('''
+        if not base.is_implicit():
+            ret += mcgen('''
     /* Own members: */
 ''')
     ret += gen_struct_members(members)
@@ -238,7 +240,7 @@ class QAPISchemaGenTypeVisitor(QAPISchemaVisitor):
     def visit_object_type(self, name, info, base, members, variants):
         self._fwdecl += gen_fwd_object_or_array(name)
         self.decl += gen_object(name, base, members, variants)
-        if base:
+        if base and not base.is_implicit():
             self.decl += gen_upcast(name, base)
         self._gen_type_cleanup(name)

diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py
index a17ecc1..aa244cd 100644
--- a/scripts/qapi-visit.py
+++ b/scripts/qapi-visit.py
@@ -34,13 +34,12 @@ void visit_type_%(c_name)s_members(Visitor *v, %(c_name)s *obj, Error **errp);
                  c_name=c_name(name))


-def gen_visit_members_call(typ, direct_name, implicit_name=None):
+def gen_visit_members_call(typ, direct_name, implicit_name):
     ret = ''
     assert isinstance(typ, QAPISchemaObjectType)
     if typ.is_empty():
         pass
     elif typ.is_implicit():
-        assert implicit_name
         assert not typ.variants
         ret += gen_visit_members(typ.members, prefix=implicit_name)
     else:
@@ -63,7 +62,8 @@ void visit_type_%(c_name)s_members(Visitor *v, %(c_name)s *obj, Error **errp)
                 c_name=c_name(name))

     if base:
-        ret += gen_visit_members_call(base, '(%s *)obj' % base.c_name())
+        ret += gen_visit_members_call(base, 'qapi_%s_base(obj)' % c_name(name),
+                                      'obj->')

     ret += gen_visit_members(members, prefix='obj->')

diff --git a/docs/qapi-code-gen.txt b/docs/qapi-code-gen.txt
index 2519c07..1c8f113 100644
--- a/docs/qapi-code-gen.txt
+++ b/docs/qapi-code-gen.txt
@@ -283,7 +283,7 @@ better than open-coding the field to be type 'str'.
 === Union types ===

 Usage: { 'union': STRING, 'data': DICT }
-or:    { 'union': STRING, 'data': DICT, 'base': STRUCT-NAME,
+or:    { 'union': STRING, 'data': DICT, 'base': STRUCT-NAME-OR-DICT,
          'discriminator': ENUM-MEMBER-OF-BASE }

 Union types are used to let the user choose between several different
@@ -319,13 +319,16 @@ an implicit C enum 'NameKind' is created, corresponding to the union
 the union can be named 'max', as this would collide with the implicit
 enum.  The value for each branch can be of any type.

-A flat union definition specifies a struct as its base, and
-avoids nesting on the wire.  All branches of the union must be
-complex types, and the top-level fields of the union dictionary on
-the wire will be combination of fields from both the base type and the
-appropriate branch type (when merging two dictionaries, there must be
-no keys in common).  The 'discriminator' field must be the name of an
-enum-typed member of the base struct.
+A flat union definition avoids nesting on the wire, and specifies a
+set of common fields that occur in all variants of the union.  The
+'base' key must specifiy either a type name (the type must be a
+struct, not a union), or a dictionary representing an anonymous type.
+All branches of the union must be complex types, and the top-level
+fields of the union dictionary on the wire will be combination of
+fields from both the base type and the appropriate branch type (when
+merging two dictionaries, there must be no keys in common).  The
+'discriminator' field must be the name of an enum-typed member of the
+base struct.

 The following example enhances the above simple union example by
 adding a common field 'readonly', renaming the discriminator to
@@ -333,10 +336,8 @@ something more applicable, and reducing the number of {} required on
 the wire:

  { 'enum': 'BlockdevDriver', 'data': [ 'file', 'qcow2' ] }
- { 'struct': 'BlockdevCommonOptions',
-   'data': { 'driver': 'BlockdevDriver', 'readonly': 'bool' } }
  { 'union': 'BlockdevOptions',
-   'base': 'BlockdevCommonOptions',
+   'base': { 'driver': 'BlockdevDriver', 'readonly': 'bool' },
    'discriminator': 'driver',
    'data': { 'file': 'FileOptions',
              'qcow2': 'Qcow2Options' } }
@@ -354,7 +355,7 @@ code generator can ensure that branches exist for all values of the
 enum (although the order of the keys need not match the declaration of
 the enum).  In the resulting generated C data types, a flat union is
 represented as a struct with the base member fields included directly,
-and then a union of structures for each branch of the struct.
+and then a union of pointers to structures for each branch of the struct.

 A simple union can always be re-written as a flat union where the base
 class has a single member named 'type', and where each branch of the
@@ -365,10 +366,9 @@ union has a struct with a single member named 'data'.  That is,
 is identical on the wire to:

  { 'enum': 'Enum', 'data': ['one', 'two'] }
- { 'struct': 'Base', 'data': { 'type': 'Enum' } }
  { 'struct': 'Branch1', 'data': { 'data': 'str' } }
  { 'struct': 'Branch2', 'data': { 'data': 'int' } }
- { 'union': 'Flat', 'base': 'Base', 'discriminator': 'type',
+ { 'union': 'Flat': 'base': { 'type': 'Enum' }, 'discriminator': 'type',
    'data': { 'one': 'Branch1', 'two': 'Branch2' } }


diff --git a/tests/qapi-schema/flat-union-bad-base.err b/tests/qapi-schema/flat-union-bad-base.err
index 79b8a71..bee24a2 100644
--- a/tests/qapi-schema/flat-union-bad-base.err
+++ b/tests/qapi-schema/flat-union-bad-base.err
@@ -1 +1 @@
-tests/qapi-schema/flat-union-bad-base.json:9: 'base' for union 'TestUnion' should be a type name
+tests/qapi-schema/flat-union-bad-base.json:8: 'string' (member of TestTypeA) collides with 'string' (base of TestUnion)
diff --git a/tests/qapi-schema/flat-union-bad-base.json b/tests/qapi-schema/flat-union-bad-base.json
index e2e622b..74dd421 100644
--- a/tests/qapi-schema/flat-union-bad-base.json
+++ b/tests/qapi-schema/flat-union-bad-base.json
@@ -1,5 +1,4 @@
-# we require the base to be an existing struct
-# TODO: should we allow an anonymous inline base type?
+# we allow anonymous base, but enforce no duplicate keys
 { 'enum': 'TestEnum',
   'data': [ 'value1', 'value2' ] }
 { 'struct': 'TestTypeA',
@@ -7,7 +6,7 @@
 { 'struct': 'TestTypeB',
   'data': { 'integer': 'int' } }
 { 'union': 'TestUnion',
-  'base': { 'enum1': 'TestEnum', 'kind': 'str' },
+  'base': { 'enum1': 'TestEnum', 'string': 'str' },
   'discriminator': 'enum1',
   'data': { 'value1': 'TestTypeA',
             'value2': 'TestTypeB' } }
diff --git a/tests/qapi-schema/qapi-schema-test.json b/tests/qapi-schema/qapi-schema-test.json
index 33e8517..a6989d8 100644
--- a/tests/qapi-schema/qapi-schema-test.json
+++ b/tests/qapi-schema/qapi-schema-test.json
@@ -75,14 +75,10 @@
   'base': 'UserDefZero',
   'data': { 'string': 'str', 'enum1': 'EnumOne' } }

-{ 'struct': 'UserDefUnionBase2',
-  'base': 'UserDefZero',
-  'data': { 'string': 'str', 'enum1': 'QEnumTwo' } }
-
 # this variant of UserDefFlatUnion defaults to a union that uses fields with
 # allocated types to test corner cases in the cleanup/dealloc visitor
 { 'union': 'UserDefFlatUnion2',
-  'base': 'UserDefUnionBase2',
+  'base': { 'string': 'str', 'enum1': 'QEnumTwo' },
   'discriminator': 'enum1',
   'data': { 'value1' : 'UserDefC', # intentional forward reference
             'value2' : 'UserDefB' } }
diff --git a/tests/qapi-schema/qapi-schema-test.out b/tests/qapi-schema/qapi-schema-test.out
index 6b97fa5..4ba347e 100644
--- a/tests/qapi-schema/qapi-schema-test.out
+++ b/tests/qapi-schema/qapi-schema-test.out
@@ -8,6 +8,9 @@ object :obj-EVENT_D-arg
     member b: str optional=False
     member c: str optional=True
     member enum3: EnumOne optional=True
+object :obj-UserDefFlatUnion2-base
+    member string: str optional=False
+    member enum1: QEnumTwo optional=False
 object :obj-__org.qemu_x-command-arg
     member a: __org.qemu_x-EnumList optional=False
     member b: __org.qemu_x-StructList optional=False
@@ -121,7 +124,7 @@ object UserDefFlatUnion
     case value2: UserDefB
     case value3: UserDefB
 object UserDefFlatUnion2
-    base UserDefUnionBase2
+    base :obj-UserDefFlatUnion2-base
     tag enum1
     case value1: UserDefC
     case value2: UserDefB
@@ -166,10 +169,6 @@ object UserDefUnionBase
     base UserDefZero
     member string: str optional=False
     member enum1: EnumOne optional=False
-object UserDefUnionBase2
-    base UserDefZero
-    member string: str optional=False
-    member enum1: QEnumTwo optional=False
 object UserDefZero
     member integer: int optional=False
 object WrapAlternate
