diff --git a/scripts/qapi.py b/scripts/qapi.py
index 05c38c5..868f08b 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -348,11 +348,6 @@ def check_alternate(expr, expr_info):
     values = { 'MAX': '(automatic)' }
     types_seen = {}

-    if expr.get('base') is not None:
-        raise QAPIExprError(expr_info,
-                            "Alternate '%s' must not have a base"
-                            % name)
-
     # Check every branch
     for (key, value) in members.items():
         # Check for conflicts in the generated enum
@@ -414,6 +409,26 @@ def check_exprs(schema):
         elif expr.has_key('event'):
             check_event(expr, info)

+def check_keys(expr_elem, meta, required, optional=[]):
+    expr = expr_elem['expr']
+    info = expr_elem['info']
+    name = expr[meta]
+    if not isinstance(name, str):
+        raise QAPIExprError(info,
+                            "'%s' key must have a string value" % meta)
+    required = required + [ meta ]
+    for (key, value) in expr.items():
+        if not key in required and not key in optional:
+            raise QAPIExprError(info,
+                                "Unknown key '%s' in %s '%s'"
+                                % (key, meta, name))
+    for key in required:
+        if not expr.has_key(key):
+            raise QAPIExprError(info,
+                                "Key '%s' is missing from %s '%s'"
+                                % (key, meta, name))
+
+
 def parse_schema(input_file):
     # First pass: read entire file into memory
     try:
@@ -425,15 +440,30 @@ def parse_schema(input_file):
     exprs = []

     try:
-        # Next pass: learn the types.
+        # Next pass: learn the types and check for valid expression keys. At
+        # this point, top-level 'include' has already been flattened.
         for expr_elem in schema.exprs:
             expr = expr_elem['expr']
             if expr.has_key('enum'):
-                add_enum(expr['enum'], expr.get('data'))
+                check_keys(expr_elem, 'enum', ['data'])
+                add_enum(expr['enum'], expr['data'])
             elif expr.has_key('union'):
+                check_keys(expr_elem, 'union', ['data'],
+                           ['base', 'discriminator'])
                 add_union(expr)
+            elif expr.has_key('alternate'):
+                check_keys(expr_elem, 'alternate', ['data'])
             elif expr.has_key('type'):
+                check_keys(expr_elem, 'type', ['data'], ['base'])
                 add_struct(expr)
+            elif expr.has_key('command'):
+                check_keys(expr_elem, 'command', [],
+                           ['data', 'returns', 'gen', 'success-response'])
+            elif expr.has_key('event'):
+                check_keys(expr_elem, 'event', [], ['data'])
+            else:
+                raise QAPIExprError(expr_elem['info'],
+                                    "Expression is missing metatype")
             exprs.append(expr)

         # Try again for hidden UnionKind enum
diff --git a/tests/qapi-schema/alternate-base.err b/tests/qapi-schema/alternate-base.err
index 4a2566e..30d8a34 100644
--- a/tests/qapi-schema/alternate-base.err
+++ b/tests/qapi-schema/alternate-base.err
@@ -1 +1 @@
-tests/qapi-schema/alternate-base.json:4: Alternate 'Alt' must not have a base
+tests/qapi-schema/alternate-base.json:4: Unknown key 'base' in alternate 'Alt'
diff --git a/tests/qapi-schema/bad-type-dict.err b/tests/qapi-schema/bad-type-dict.err
index e69de29..0b2a2ae 100644
--- a/tests/qapi-schema/bad-type-dict.err
+++ b/tests/qapi-schema/bad-type-dict.err
@@ -0,0 +1 @@
+tests/qapi-schema/bad-type-dict.json:2: 'command' key must have a string value
diff --git a/tests/qapi-schema/bad-type-dict.exit b/tests/qapi-schema/bad-type-dict.exit
index 573541a..d00491f 100644
--- a/tests/qapi-schema/bad-type-dict.exit
+++ b/tests/qapi-schema/bad-type-dict.exit
@@ -1 +1 @@
-0
+1
diff --git a/tests/qapi-schema/bad-type-dict.json b/tests/qapi-schema/bad-type-dict.json
index 3c392a7..2a91b24 100644
--- a/tests/qapi-schema/bad-type-dict.json
+++ b/tests/qapi-schema/bad-type-dict.json
@@ -1,2 +1,2 @@
-# FIXME: we should reject an expression with a metatype that is not a string
+# we reject an expression with a metatype that is not a string
 { 'command': { } }
diff --git a/tests/qapi-schema/bad-type-dict.out b/tests/qapi-schema/bad-type-dict.out
index c62f1ed..e69de29 100644
--- a/tests/qapi-schema/bad-type-dict.out
+++ b/tests/qapi-schema/bad-type-dict.out
@@ -1,3 +0,0 @@
-[OrderedDict([('command', OrderedDict())])]
-[]
-[]
diff --git a/tests/qapi-schema/double-type.err b/tests/qapi-schema/double-type.err
index e69de29..ceb6e46 100644
--- a/tests/qapi-schema/double-type.err
+++ b/tests/qapi-schema/double-type.err
@@ -0,0 +1 @@
+tests/qapi-schema/double-type.json:2: Unknown key 'command' in type 'bar'
diff --git a/tests/qapi-schema/double-type.exit b/tests/qapi-schema/double-type.exit
index 573541a..d00491f 100644
--- a/tests/qapi-schema/double-type.exit
+++ b/tests/qapi-schema/double-type.exit
@@ -1 +1 @@
-0
+1
diff --git a/tests/qapi-schema/double-type.json b/tests/qapi-schema/double-type.json
index 6ca96b9..471623a 100644
--- a/tests/qapi-schema/double-type.json
+++ b/tests/qapi-schema/double-type.json
@@ -1,2 +1,2 @@
-# FIXME: we should reject an expression with ambiguous metatype
+# we reject an expression with ambiguous metatype
 { 'command': 'foo', 'type': 'bar', 'data': { } }
diff --git a/tests/qapi-schema/double-type.out b/tests/qapi-schema/double-type.out
index 3e244f5..e69de29 100644
--- a/tests/qapi-schema/double-type.out
+++ b/tests/qapi-schema/double-type.out
@@ -1,3 +0,0 @@
-[OrderedDict([('command', 'foo'), ('type', 'bar'), ('data', OrderedDict())])]
-[]
-[OrderedDict([('command', 'foo'), ('type', 'bar'), ('data', OrderedDict())])]
diff --git a/tests/qapi-schema/enum-missing-data.err b/tests/qapi-schema/enum-missing-data.err
index b8ccae0..ba4873a 100644
--- a/tests/qapi-schema/enum-missing-data.err
+++ b/tests/qapi-schema/enum-missing-data.err
@@ -1 +1 @@
-tests/qapi-schema/enum-missing-data.json:2: Enum 'MyEnum' requires an array for 'data'
+tests/qapi-schema/enum-missing-data.json:2: Key 'data' is missing from enum 'MyEnum'
diff --git a/tests/qapi-schema/ident-with-escape.err b/tests/qapi-schema/ident-with-escape.err
index e69de29..f7d1c55 100644
--- a/tests/qapi-schema/ident-with-escape.err
+++ b/tests/qapi-schema/ident-with-escape.err
@@ -0,0 +1 @@
+tests/qapi-schema/ident-with-escape.json:3: Expression is missing metatype
diff --git a/tests/qapi-schema/ident-with-escape.exit b/tests/qapi-schema/ident-with-escape.exit
index 573541a..d00491f 100644
--- a/tests/qapi-schema/ident-with-escape.exit
+++ b/tests/qapi-schema/ident-with-escape.exit
@@ -1 +1 @@
-0
+1
diff --git a/tests/qapi-schema/ident-with-escape.out b/tests/qapi-schema/ident-with-escape.out
index a44623f..e69de29 100644
--- a/tests/qapi-schema/ident-with-escape.out
+++ b/tests/qapi-schema/ident-with-escape.out
@@ -1,3 +0,0 @@
-[OrderedDict([('cu006fmmand', 'u0066u006fu006FA'), ('du0061ta', OrderedDict([('u0062u0061u00721', 'u0073u0074u0072')]))])]
-[]
-[]
diff --git a/tests/qapi-schema/indented-expr.json b/tests/qapi-schema/indented-expr.json
index d80af60..7115d31 100644
--- a/tests/qapi-schema/indented-expr.json
+++ b/tests/qapi-schema/indented-expr.json
@@ -1,2 +1,2 @@
-{ 'id' : 'eins' }
- { 'id' : 'zwei' }
+{ 'command' : 'eins' }
+ { 'command' : 'zwei' }
diff --git a/tests/qapi-schema/indented-expr.out b/tests/qapi-schema/indented-expr.out
index 98af89a..b5ce915 100644
--- a/tests/qapi-schema/indented-expr.out
+++ b/tests/qapi-schema/indented-expr.out
@@ -1,3 +1,3 @@
-[OrderedDict([('id', 'eins')]), OrderedDict([('id', 'zwei')])]
+[OrderedDict([('command', 'eins')]), OrderedDict([('command', 'zwei')])]
 []
 []
diff --git a/tests/qapi-schema/missing-type.err b/tests/qapi-schema/missing-type.err
index e69de29..b3e7b14 100644
--- a/tests/qapi-schema/missing-type.err
+++ b/tests/qapi-schema/missing-type.err
@@ -0,0 +1 @@
+tests/qapi-schema/missing-type.json:2: Expression is missing metatype
diff --git a/tests/qapi-schema/missing-type.exit b/tests/qapi-schema/missing-type.exit
index 573541a..d00491f 100644
--- a/tests/qapi-schema/missing-type.exit
+++ b/tests/qapi-schema/missing-type.exit
@@ -1 +1 @@
-0
+1
diff --git a/tests/qapi-schema/missing-type.json b/tests/qapi-schema/missing-type.json
index 1696f5c..ff5349d 100644
--- a/tests/qapi-schema/missing-type.json
+++ b/tests/qapi-schema/missing-type.json
@@ -1,2 +1,2 @@
-# FIXME: we should reject an expression with missing metatype
+# we reject an expression with missing metatype
 { 'data': { } }
diff --git a/tests/qapi-schema/missing-type.out b/tests/qapi-schema/missing-type.out
index 67fd4fa..e69de29 100644
--- a/tests/qapi-schema/missing-type.out
+++ b/tests/qapi-schema/missing-type.out
@@ -1,3 +0,0 @@
-[OrderedDict([('data', OrderedDict())])]
-[]
-[]
diff --git a/tests/qapi-schema/unknown-expr-key.err b/tests/qapi-schema/unknown-expr-key.err
index e69de29..0a35bfd 100644
--- a/tests/qapi-schema/unknown-expr-key.err
+++ b/tests/qapi-schema/unknown-expr-key.err
@@ -0,0 +1 @@
+tests/qapi-schema/unknown-expr-key.json:2: Unknown key 'bogus' in type 'bar'
diff --git a/tests/qapi-schema/unknown-expr-key.exit b/tests/qapi-schema/unknown-expr-key.exit
index 573541a..d00491f 100644
--- a/tests/qapi-schema/unknown-expr-key.exit
+++ b/tests/qapi-schema/unknown-expr-key.exit
@@ -1 +1 @@
-0
+1
diff --git a/tests/qapi-schema/unknown-expr-key.json b/tests/qapi-schema/unknown-expr-key.json
index 1e9282d..ba7bdf3 100644
--- a/tests/qapi-schema/unknown-expr-key.json
+++ b/tests/qapi-schema/unknown-expr-key.json
@@ -1,2 +1,2 @@
-# FIXME: we should reject an expression with unknown top-level keys
+# we reject an expression with unknown top-level keys
 { 'type': 'bar', 'data': { 'string': 'str'}, 'bogus': { } }
diff --git a/tests/qapi-schema/unknown-expr-key.out b/tests/qapi-schema/unknown-expr-key.out
index c93f020..e69de29 100644
--- a/tests/qapi-schema/unknown-expr-key.out
+++ b/tests/qapi-schema/unknown-expr-key.out
@@ -1,3 +0,0 @@
-[OrderedDict([('type', 'bar'), ('data', OrderedDict([('string', 'str')])), ('bogus', OrderedDict())])]
-[]
-[OrderedDict([('type', 'bar'), ('data', OrderedDict([('string', 'str')])), ('bogus', OrderedDict())])]
