diff --git a/scripts/qapi.py b/scripts/qapi.py
index 8fbc45f..bf243fa 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -19,8 +19,15 @@ import sys
 builtin_types = [
     'str', 'int', 'number', 'bool',
     'int8', 'int16', 'int32', 'int64',
-    'uint8', 'uint16', 'uint32', 'uint64'
+    'uint8', 'uint16', 'uint32', 'uint64',
+    'size'
 ]
+enum_types = []
+struct_types = []
+union_types = []
+all_types = {}
+commands = []
+events = ['MAX']

 builtin_type_qtypes = {
     'str':      'QTYPE_QSTRING',
@@ -248,8 +255,22 @@ def discriminator_find_enum_define(expr):

     return find_enum(discriminator_type)

+def check_command(expr, expr_info):
+    global commands
+    name = expr['command']
+    if name in commands:
+        raise QAPIExprError(expr_info,
+                            "command '%s' is already defined" % name)
+    commands.append(name)
+
 def check_event(expr, expr_info):
+    global events
+    name = expr['event']
     params = expr.get('data')
+    if name in events:
+        raise QAPIExprError(expr_info,
+                            "event '%s' is already defined" % name)
+    events.append(name)
     if params:
         for argname, argentry, optional, structured in parse_args(params):
             if structured:
@@ -347,6 +368,8 @@ def check_exprs(schema):
             check_event(expr, info)
         if expr.has_key('enum'):
             check_enum(expr, info)
+        if expr.has_key('command'):
+            check_command(expr, info)

 def check_keys(expr_elem, meta, required, optional=[]):
     expr = expr_elem['expr']
@@ -370,6 +393,9 @@ def check_keys(expr_elem, meta, required, optional=[]):


 def parse_schema(input_file):
+    global all_types
+    exprs = []
+
     # First pass: read entire file into memory
     try:
         schema = QAPISchema(open(input_file, "r"))
@@ -377,16 +403,17 @@ def parse_schema(input_file):
         print >>sys.stderr, e
         exit(1)

-    exprs = []
-
     try:
         # Next pass: learn the types and check for valid expression keys. At
         # this point, top-level 'include' has already been flattened.
+        for builtin in builtin_types:
+            all_types[builtin] = 'built-in'
         for expr_elem in schema.exprs:
             expr = expr_elem['expr']
+            info = expr_elem['info']
             if expr.has_key('enum'):
                 check_keys(expr_elem, 'enum', ['data'])
-                add_enum(expr['enum'], expr['data'])
+                add_enum(expr['enum'], info, expr['data'])
             elif expr.has_key('union'):
                 # Two styles of union, based on discriminator
                 discriminator = expr.get('discriminator')
@@ -395,10 +422,10 @@ def parse_schema(input_file):
                 else:
                     check_keys(expr_elem, 'union', ['data'],
                                ['base', 'discriminator'])
-                add_union(expr)
+                add_union(expr, info)
             elif expr.has_key('type'):
                 check_keys(expr_elem, 'type', ['data'], ['base'])
-                add_struct(expr)
+                add_struct(expr, info)
             elif expr.has_key('command'):
                 check_keys(expr_elem, 'command', [],
                            ['data', 'returns', 'gen', 'success-response'])
@@ -414,7 +441,7 @@ def parse_schema(input_file):
             expr = expr_elem['expr']
             if expr.has_key('union'):
                 if not discriminator_find_enum_define(expr):
-                    add_enum('%sKind' % expr['union'])
+                    add_enum('%sKind' % expr['union'], expr_elem['info'])

         # Final pass - validate that exprs make sense
         check_exprs(schema)
@@ -508,12 +535,15 @@ def type_name(name):
         return c_list_type(name[0])
     return name

-enum_types = []
-struct_types = []
-union_types = []
-
-def add_struct(definition):
+def add_struct(definition, info):
     global struct_types
+    global all_types
+    name = definition['type']
+    if name in all_types:
+        raise QAPIExprError(info,
+                            "%s '%s' is already defined"
+                            %(all_types[name], name))
+    all_types[name] = 'struct'
     struct_types.append(definition)

 def find_struct(name):
@@ -523,8 +553,15 @@ def find_struct(name):
             return struct
     return None

-def add_union(definition):
+def add_union(definition, info):
     global union_types
+    global all_types
+    name = definition['union']
+    if name in all_types:
+        raise QAPIExprError(info,
+                            "%s '%s' is already defined"
+                            %(all_types[name], name))
+    all_types[name] = 'union'
     union_types.append(definition)

 def find_union(name):
@@ -534,8 +571,14 @@ def find_union(name):
             return union
     return None

-def add_enum(name, enum_values = None):
+def add_enum(name, info, enum_values = None):
     global enum_types
+    global all_types
+    if name in all_types:
+        raise QAPIExprError(info,
+                            "%s '%s' is already defined"
+                            %(all_types[name], name))
+    all_types[name] = 'enum'
     enum_types.append({"enum_name": name, "enum_values": enum_values})

 def find_enum(name):
diff --git a/tests/qapi-schema/redefined-builtin.err b/tests/qapi-schema/redefined-builtin.err
index e69de29..b275722 100644
--- a/tests/qapi-schema/redefined-builtin.err
+++ b/tests/qapi-schema/redefined-builtin.err
@@ -0,0 +1 @@
+tests/qapi-schema/redefined-builtin.json:2: built-in 'size' is already defined
diff --git a/tests/qapi-schema/redefined-builtin.exit b/tests/qapi-schema/redefined-builtin.exit
index 573541a..d00491f 100644
--- a/tests/qapi-schema/redefined-builtin.exit
+++ b/tests/qapi-schema/redefined-builtin.exit
@@ -1 +1 @@
-0
+1
diff --git a/tests/qapi-schema/redefined-builtin.json b/tests/qapi-schema/redefined-builtin.json
index a10050d..df328cc 100644
--- a/tests/qapi-schema/redefined-builtin.json
+++ b/tests/qapi-schema/redefined-builtin.json
@@ -1,2 +1,2 @@
-# FIXME: we should reject types that duplicate builtin names
+# we reject types that duplicate builtin names
 { 'type': 'size', 'data': { 'myint': 'size' } }
diff --git a/tests/qapi-schema/redefined-builtin.out b/tests/qapi-schema/redefined-builtin.out
index b0a9aea..e69de29 100644
--- a/tests/qapi-schema/redefined-builtin.out
+++ b/tests/qapi-schema/redefined-builtin.out
@@ -1,3 +0,0 @@
-[OrderedDict([('type', 'size'), ('data', OrderedDict([('myint', 'size')]))])]
-[]
-[OrderedDict([('type', 'size'), ('data', OrderedDict([('myint', 'size')]))])]
diff --git a/tests/qapi-schema/redefined-command.err b/tests/qapi-schema/redefined-command.err
index e69de29..82ae256 100644
--- a/tests/qapi-schema/redefined-command.err
+++ b/tests/qapi-schema/redefined-command.err
@@ -0,0 +1 @@
+tests/qapi-schema/redefined-command.json:3: command 'foo' is already defined
diff --git a/tests/qapi-schema/redefined-command.exit b/tests/qapi-schema/redefined-command.exit
index 573541a..d00491f 100644
--- a/tests/qapi-schema/redefined-command.exit
+++ b/tests/qapi-schema/redefined-command.exit
@@ -1 +1 @@
-0
+1
diff --git a/tests/qapi-schema/redefined-command.json b/tests/qapi-schema/redefined-command.json
index d8c9975..247e401 100644
--- a/tests/qapi-schema/redefined-command.json
+++ b/tests/qapi-schema/redefined-command.json
@@ -1,3 +1,3 @@
-# FIXME: we should reject commands defined more than once
+# we reject commands defined more than once
 { 'command': 'foo', 'data': { 'one': 'str' } }
 { 'command': 'foo', 'data': { '*two': 'str' } }
diff --git a/tests/qapi-schema/redefined-command.out b/tests/qapi-schema/redefined-command.out
index 44ddba6..e69de29 100644
--- a/tests/qapi-schema/redefined-command.out
+++ b/tests/qapi-schema/redefined-command.out
@@ -1,4 +0,0 @@
-[OrderedDict([('command', 'foo'), ('data', OrderedDict([('one', 'str')]))]),
- OrderedDict([('command', 'foo'), ('data', OrderedDict([('*two', 'str')]))])]
-[]
-[]
diff --git a/tests/qapi-schema/redefined-event.err b/tests/qapi-schema/redefined-event.err
index e69de29..35429cb 100644
--- a/tests/qapi-schema/redefined-event.err
+++ b/tests/qapi-schema/redefined-event.err
@@ -0,0 +1 @@
+tests/qapi-schema/redefined-event.json:3: event 'EVENT_A' is already defined
diff --git a/tests/qapi-schema/redefined-event.exit b/tests/qapi-schema/redefined-event.exit
index 573541a..d00491f 100644
--- a/tests/qapi-schema/redefined-event.exit
+++ b/tests/qapi-schema/redefined-event.exit
@@ -1 +1 @@
-0
+1
diff --git a/tests/qapi-schema/redefined-event.json b/tests/qapi-schema/redefined-event.json
index 152cce7..7717e91 100644
--- a/tests/qapi-schema/redefined-event.json
+++ b/tests/qapi-schema/redefined-event.json
@@ -1,3 +1,3 @@
-# FIXME: we should reject duplicate events
+# we reject duplicate events
 { 'event': 'EVENT_A', 'data': { 'myint': 'int' } }
 { 'event': 'EVENT_A', 'data': { 'myint': 'int' } }
diff --git a/tests/qapi-schema/redefined-event.out b/tests/qapi-schema/redefined-event.out
index 261b183..e69de29 100644
--- a/tests/qapi-schema/redefined-event.out
+++ b/tests/qapi-schema/redefined-event.out
@@ -1,4 +0,0 @@
-[OrderedDict([('event', 'EVENT_A'), ('data', OrderedDict([('myint', 'int')]))]),
- OrderedDict([('event', 'EVENT_A'), ('data', OrderedDict([('myint', 'int')]))])]
-[]
-[]
diff --git a/tests/qapi-schema/redefined-type.err b/tests/qapi-schema/redefined-type.err
index e69de29..06ea78c 100644
--- a/tests/qapi-schema/redefined-type.err
+++ b/tests/qapi-schema/redefined-type.err
@@ -0,0 +1 @@
+tests/qapi-schema/redefined-type.json:3: struct 'foo' is already defined
diff --git a/tests/qapi-schema/redefined-type.exit b/tests/qapi-schema/redefined-type.exit
index 573541a..d00491f 100644
--- a/tests/qapi-schema/redefined-type.exit
+++ b/tests/qapi-schema/redefined-type.exit
@@ -1 +1 @@
-0
+1
diff --git a/tests/qapi-schema/redefined-type.json b/tests/qapi-schema/redefined-type.json
index 7972194..e6a5f24 100644
--- a/tests/qapi-schema/redefined-type.json
+++ b/tests/qapi-schema/redefined-type.json
@@ -1,3 +1,3 @@
-# FIXME: we should reject types defined more than once
+# we reject types defined more than once
 { 'type': 'foo', 'data': { 'one': 'str' } }
 { 'enum': 'foo', 'data': [ 'two' ] }
diff --git a/tests/qapi-schema/redefined-type.out b/tests/qapi-schema/redefined-type.out
index b509e57..e69de29 100644
--- a/tests/qapi-schema/redefined-type.out
+++ b/tests/qapi-schema/redefined-type.out
@@ -1,4 +0,0 @@
-[OrderedDict([('type', 'foo'), ('data', OrderedDict([('one', 'str')]))]),
- OrderedDict([('enum', 'foo'), ('data', ['two'])])]
-[{'enum_name': 'foo', 'enum_values': ['two']}]
-[OrderedDict([('type', 'foo'), ('data', OrderedDict([('one', 'str')]))])]
