diff --git a/tests/Makefile b/tests/Makefile
index 164dea3..49fdbe2 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -241,6 +241,7 @@ qapi-schema += args-invalid.json
 qapi-schema += args-member-array-bad.json
 qapi-schema += args-member-array.json
 qapi-schema += args-member-unknown.json
+qapi-schema += args-name-clash.json
 qapi-schema += args-union.json
 qapi-schema += args-unknown.json
 qapi-schema += bad-base.json
@@ -276,7 +277,9 @@ qapi-schema += flat-union-bad-base.json
 qapi-schema += flat-union-bad-discriminator.json
 qapi-schema += flat-union-base-any.json
 qapi-schema += flat-union-base-union.json
-qapi-schema += flat-union-branch-clash.json
+qapi-schema += flat-union-clash-branch.json
+qapi-schema += flat-union-clash-member.json
+qapi-schema += flat-union-clash-type.json
 qapi-schema += flat-union-inline.json
 qapi-schema += flat-union-int-branch.json
 qapi-schema += flat-union-invalid-branch-key.json
@@ -318,6 +321,7 @@ qapi-schema += returns-dict.json
 qapi-schema += returns-int.json
 qapi-schema += returns-unknown.json
 qapi-schema += returns-whitelist.json
+qapi-schema += struct-base-clash-base.json
 qapi-schema += struct-base-clash-deep.json
 qapi-schema += struct-base-clash.json
 qapi-schema += struct-data-invalid.json
@@ -331,6 +335,9 @@ qapi-schema += unclosed-string.json
 qapi-schema += unicode-str.json
 qapi-schema += union-bad-branch.json
 qapi-schema += union-base-no-discriminator.json
+qapi-schema += union-clash-branches.json
+qapi-schema += union-clash-data.json
+qapi-schema += union-clash-type.json
 qapi-schema += union-invalid-base.json
 qapi-schema += union-max.json
 qapi-schema += union-optional-branch.json
diff --git a/tests/qapi-schema/alternate-clash.err b/tests/qapi-schema/alternate-clash.err
index 51bea3e..a475ab6 100644
--- a/tests/qapi-schema/alternate-clash.err
+++ b/tests/qapi-schema/alternate-clash.err
@@ -1 +1 @@
-tests/qapi-schema/alternate-clash.json:2: Alternate 'Alt1' member 'ONE' clashes with 'one'
+tests/qapi-schema/alternate-clash.json:7: Alternate 'Alt1' member 'a_b' clashes with 'a-b'
diff --git a/tests/qapi-schema/alternate-clash.json b/tests/qapi-schema/alternate-clash.json
index 3947935..6d73bc5 100644
--- a/tests/qapi-schema/alternate-clash.json
+++ b/tests/qapi-schema/alternate-clash.json
@@ -1,3 +1,8 @@
-# we detect C enum collisions in an alternate
+# Alternate branch name collision
+# Reject an alternate that would result in a collision in generated C
+# names (this would try to generate two enum values 'ALT1_KIND_A_B').
+# TODO: In the future, if alternates are simplified to not generate
+# the implicit Alt1Kind enum, we would still have a collision with the
+# resulting C union trying to have two members named 'a_b'.
 { 'alternate': 'Alt1',
-  'data': { 'one': 'str', 'ONE': 'int' } }
+  'data': { 'a-b': 'str', 'a_b': 'int' } }
diff --git a/tests/qapi-schema/flat-union-branch-clash.out b/tests/qapi-schema/args-name-clash.err
similarity index 100%
rename from tests/qapi-schema/flat-union-branch-clash.out
rename to tests/qapi-schema/args-name-clash.err
diff --git a/tests/qapi-schema/args-name-clash.exit b/tests/qapi-schema/args-name-clash.exit
new file mode 100644
index 0000000..573541a
--- /dev/null
+++ b/tests/qapi-schema/args-name-clash.exit
@@ -0,0 +1 @@
+0
diff --git a/tests/qapi-schema/args-name-clash.json b/tests/qapi-schema/args-name-clash.json
new file mode 100644
index 0000000..9e8f889
--- /dev/null
+++ b/tests/qapi-schema/args-name-clash.json
@@ -0,0 +1,5 @@
+# C member name collision
+# FIXME - This parses, but fails to compile, because the C struct is given
+# two 'a_b' members.  Either reject this at parse time, or munge the C names
+# to avoid the collision.
+{ 'command': 'oops', 'data': { 'a-b': 'str', 'a_b': 'str' } }
diff --git a/tests/qapi-schema/args-name-clash.out b/tests/qapi-schema/args-name-clash.out
new file mode 100644
index 0000000..9b2f6e4
--- /dev/null
+++ b/tests/qapi-schema/args-name-clash.out
@@ -0,0 +1,6 @@
+object :empty
+object :obj-oops-arg
+    member a-b: str optional=False
+    member a_b: str optional=False
+command oops :obj-oops-arg -> None
+   gen=True success_response=True
diff --git a/tests/qapi-schema/duplicate-key.err b/tests/qapi-schema/duplicate-key.err
index 768b276..6d02f83 100644
--- a/tests/qapi-schema/duplicate-key.err
+++ b/tests/qapi-schema/duplicate-key.err
@@ -1 +1 @@
-tests/qapi-schema/duplicate-key.json:2:10: Duplicate key "key"
+tests/qapi-schema/duplicate-key.json:3:10: Duplicate key "key"
diff --git a/tests/qapi-schema/duplicate-key.json b/tests/qapi-schema/duplicate-key.json
index 1b55d88..14ac0e8 100644
--- a/tests/qapi-schema/duplicate-key.json
+++ b/tests/qapi-schema/duplicate-key.json
@@ -1,2 +1,3 @@
+# QAPI cannot include the same key more than once in any {}
 { 'key': 'value',
   'key': 'value' }
diff --git a/tests/qapi-schema/flat-union-base-union.err b/tests/qapi-schema/flat-union-base-union.err
index ede9859..28725ed 100644
--- a/tests/qapi-schema/flat-union-base-union.err
+++ b/tests/qapi-schema/flat-union-base-union.err
@@ -1 +1 @@
-tests/qapi-schema/flat-union-base-union.json:11: Base 'UnionBase' is not a valid struct
+tests/qapi-schema/flat-union-base-union.json:14: Base 'UnionBase' is not a valid struct
diff --git a/tests/qapi-schema/flat-union-base-union.json b/tests/qapi-schema/flat-union-base-union.json
index 6a8ea68..98b4eba 100644
--- a/tests/qapi-schema/flat-union-base-union.json
+++ b/tests/qapi-schema/flat-union-base-union.json
@@ -1,4 +1,7 @@
-# we require the base to be a struct
+# For now, we require the base to be a struct without variants
+# TODO: It would be possible to allow a union as a base, as long as all
+# permutations of QMP names exposed by base do not clash with any QMP
+# member names added by local variants.
 { 'enum': 'TestEnum',
   'data': [ 'value1', 'value2' ] }
 { 'struct': 'TestTypeA',
diff --git a/tests/qapi-schema/flat-union-branch-clash.err b/tests/qapi-schema/flat-union-branch-clash.err
deleted file mode 100644
index f112766..0000000
--- a/tests/qapi-schema/flat-union-branch-clash.err
+++ /dev/null
@@ -1 +0,0 @@
-tests/qapi-schema/flat-union-branch-clash.json:10: Member name 'name' of branch 'value1' clashes with base 'Base'
diff --git a/tests/qapi-schema/flat-union-clash-branch.err b/tests/qapi-schema/flat-union-clash-branch.err
new file mode 100644
index 0000000..e69de29
diff --git a/tests/qapi-schema/flat-union-clash-branch.exit b/tests/qapi-schema/flat-union-clash-branch.exit
new file mode 100644
index 0000000..573541a
--- /dev/null
+++ b/tests/qapi-schema/flat-union-clash-branch.exit
@@ -0,0 +1 @@
+0
diff --git a/tests/qapi-schema/flat-union-clash-branch.json b/tests/qapi-schema/flat-union-clash-branch.json
new file mode 100644
index 0000000..e593336
--- /dev/null
+++ b/tests/qapi-schema/flat-union-clash-branch.json
@@ -0,0 +1,18 @@
+# Flat union branch name collision
+# FIXME: this parses, but then fails to compile due to a duplicate 'c_d'
+# (one from the base member, the other from the branch name).  We should
+# either reject the collision at parse time, or munge the generated branch
+# name to allow this to compile.
+{ 'enum': 'TestEnum',
+  'data': [ 'base', 'c-d' ] }
+{ 'struct': 'Base',
+  'data': { 'enum1': 'TestEnum', '*c_d': 'str' } }
+{ 'struct': 'Branch1',
+  'data': { 'string': 'str' } }
+{ 'struct': 'Branch2',
+  'data': { 'value': 'int' } }
+{ 'union': 'TestUnion',
+  'base': 'Base',
+  'discriminator': 'enum1',
+  'data': { 'base': 'Branch1',
+            'c-d': 'Branch2' } }
diff --git a/tests/qapi-schema/flat-union-clash-branch.out b/tests/qapi-schema/flat-union-clash-branch.out
new file mode 100644
index 0000000..8e0da73
--- /dev/null
+++ b/tests/qapi-schema/flat-union-clash-branch.out
@@ -0,0 +1,14 @@
+object :empty
+object Base
+    member enum1: TestEnum optional=False
+    member c_d: str optional=True
+object Branch1
+    member string: str optional=False
+object Branch2
+    member value: int optional=False
+enum TestEnum ['base', 'c-d']
+object TestUnion
+    base Base
+    tag enum1
+    case base: Branch1
+    case c-d: Branch2
diff --git a/tests/qapi-schema/flat-union-clash-member.err b/tests/qapi-schema/flat-union-clash-member.err
new file mode 100644
index 0000000..2f0397a
--- /dev/null
+++ b/tests/qapi-schema/flat-union-clash-member.err
@@ -0,0 +1 @@
+tests/qapi-schema/flat-union-clash-member.json:11: Member name 'name' of branch 'value1' clashes with base 'Base'
diff --git a/tests/qapi-schema/flat-union-branch-clash.exit b/tests/qapi-schema/flat-union-clash-member.exit
similarity index 100%
rename from tests/qapi-schema/flat-union-branch-clash.exit
rename to tests/qapi-schema/flat-union-clash-member.exit
diff --git a/tests/qapi-schema/flat-union-branch-clash.json b/tests/qapi-schema/flat-union-clash-member.json
similarity index 77%
rename from tests/qapi-schema/flat-union-branch-clash.json
rename to tests/qapi-schema/flat-union-clash-member.json
index 8fb054f..9efc771 100644
--- a/tests/qapi-schema/flat-union-branch-clash.json
+++ b/tests/qapi-schema/flat-union-clash-member.json
@@ -1,4 +1,5 @@
-# we check for no duplicate keys between branches and base
+# We check for no duplicate keys between branch members and base
+# base's member 'name' clashes with Branch1's
 { 'enum': 'TestEnum',
   'data': [ 'value1', 'value2' ] }
 { 'struct': 'Base',
diff --git a/tests/qapi-schema/flat-union-clash-member.out b/tests/qapi-schema/flat-union-clash-member.out
new file mode 100644
index 0000000..e69de29
diff --git a/tests/qapi-schema/flat-union-clash-type.err b/tests/qapi-schema/flat-union-clash-type.err
new file mode 100644
index 0000000..6e64d1d
--- /dev/null
+++ b/tests/qapi-schema/flat-union-clash-type.err
@@ -0,0 +1,16 @@
+Traceback (most recent call last):
+  File "tests/qapi-schema/test-qapi.py", line 55, in <module>
+    schema = QAPISchema(sys.argv[1])
+  File "scripts/qapi.py", line 1116, in __init__
+    self.check()
+  File "scripts/qapi.py", line 1299, in check
+    ent.check(self)
+  File "scripts/qapi.py", line 962, in check
+    self.variants.check(schema, members, seen)
+  File "scripts/qapi.py", line 1024, in check
+    v.check(schema, self.tag_member.type, vseen)
+  File "scripts/qapi.py", line 1032, in check
+    QAPISchemaObjectTypeMember.check(self, schema, [], seen)
+  File "scripts/qapi.py", line 994, in check
+    assert self.name not in seen
+AssertionError
diff --git a/tests/qapi-schema/flat-union-clash-type.exit b/tests/qapi-schema/flat-union-clash-type.exit
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/tests/qapi-schema/flat-union-clash-type.exit
@@ -0,0 +1 @@
+1
diff --git a/tests/qapi-schema/flat-union-clash-type.json b/tests/qapi-schema/flat-union-clash-type.json
new file mode 100644
index 0000000..3db6ea0
--- /dev/null
+++ b/tests/qapi-schema/flat-union-clash-type.json
@@ -0,0 +1,16 @@
+# Flat union branch 'type'
+# FIXME: this triggers an assertion failure. But even with that fixed,
+# we would have a clash in generated C, between the member 'type'
+# inherited from 'Base' and the branch name 'type' within the
+# union. We should either reject this, or munge the generated C to let
+# it compile.
+{ 'enum': 'TestEnum',
+  'data': [ 'type' ] }
+{ 'struct': 'Base',
+  'data': { 'type': 'TestEnum' } }
+{ 'struct': 'Branch1',
+  'data': { 'string': 'str' } }
+{ 'union': 'TestUnion',
+  'base': 'Base',
+  'discriminator': 'type',
+  'data': { 'type': 'Branch1' } }
diff --git a/tests/qapi-schema/flat-union-clash-type.out b/tests/qapi-schema/flat-union-clash-type.out
new file mode 100644
index 0000000..e69de29
diff --git a/tests/qapi-schema/qapi-schema-test.json b/tests/qapi-schema/qapi-schema-test.json
index 6897a6e..c511338 100644
--- a/tests/qapi-schema/qapi-schema-test.json
+++ b/tests/qapi-schema/qapi-schema-test.json
@@ -32,11 +32,14 @@
             'dict1': 'UserDefTwoDict' } }
 
 # for testing unions
+# Among other things, test that a name collision between branches does
+# not cause any problems (since only one branch can be in use at a time),
+# by intentionally using two branches that both have a C member 'a_b'
 { 'struct': 'UserDefA',
-  'data': { 'boolean': 'bool' } }
+  'data': { 'boolean': 'bool', '*a_b': 'int' } }
 
 { 'struct': 'UserDefB',
-  'data': { 'intb': 'int' } }
+  'data': { 'intb': 'int', '*a-b': 'bool' } }
 
 { 'union': 'UserDefFlatUnion',
   'base': 'UserDefUnionBase',   # intentional forward reference
diff --git a/tests/qapi-schema/qapi-schema-test.out b/tests/qapi-schema/qapi-schema-test.out
index 1f6e858..28a0b3c 100644
--- a/tests/qapi-schema/qapi-schema-test.out
+++ b/tests/qapi-schema/qapi-schema-test.out
@@ -71,6 +71,7 @@ enum QEnumTwo ['value1', 'value2']
     prefix QENUM_TWO
 object UserDefA
     member boolean: bool optional=False
+    member a_b: int optional=True
 alternate UserDefAlternate
     case uda: UserDefA
     case s: str
@@ -78,6 +79,7 @@ alternate UserDefAlternate
 enum UserDefAlternateKind ['uda', 's', 'i']
 object UserDefB
     member intb: int optional=False
+    member a-b: bool optional=True
 object UserDefC
     member string1: str optional=False
     member string2: str optional=False
diff --git a/tests/qapi-schema/struct-base-clash-base.err b/tests/qapi-schema/struct-base-clash-base.err
new file mode 100644
index 0000000..e69de29
diff --git a/tests/qapi-schema/struct-base-clash-base.exit b/tests/qapi-schema/struct-base-clash-base.exit
new file mode 100644
index 0000000..573541a
--- /dev/null
+++ b/tests/qapi-schema/struct-base-clash-base.exit
@@ -0,0 +1 @@
+0
diff --git a/tests/qapi-schema/struct-base-clash-base.json b/tests/qapi-schema/struct-base-clash-base.json
new file mode 100644
index 0000000..0c84025
--- /dev/null
+++ b/tests/qapi-schema/struct-base-clash-base.json
@@ -0,0 +1,9 @@
+# Struct member 'base'
+# FIXME: this parses, but then fails to compile due to a duplicate 'base'
+# (one explicit in QMP, the other used to box the base class members).
+# We should either reject the collision at parse time, or change the
+# generated struct to allow this to compile.
+{ 'struct': 'Base', 'data': {} }
+{ 'struct': 'Sub',
+  'base': 'Base',
+  'data': { 'base': 'str' } }
diff --git a/tests/qapi-schema/struct-base-clash-base.out b/tests/qapi-schema/struct-base-clash-base.out
new file mode 100644
index 0000000..e69a416
--- /dev/null
+++ b/tests/qapi-schema/struct-base-clash-base.out
@@ -0,0 +1,5 @@
+object :empty
+object Base
+object Sub
+    base Base
+    member base: str optional=False
diff --git a/tests/qapi-schema/struct-base-clash-deep.err b/tests/qapi-schema/struct-base-clash-deep.err
index e3e9f8d..f7a25a3 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:7: Member name 'name' clashes with base 'Base'
+tests/qapi-schema/struct-base-clash-deep.json:10: Member name 'name' clashes with base 'Base'
diff --git a/tests/qapi-schema/struct-base-clash-deep.json b/tests/qapi-schema/struct-base-clash-deep.json
index 552fe94..fa873ab 100644
--- a/tests/qapi-schema/struct-base-clash-deep.json
+++ b/tests/qapi-schema/struct-base-clash-deep.json
@@ -1,4 +1,7 @@
-# we check for no duplicate keys with indirect base
+# Reject attempts to duplicate QMP members
+# Here, 'name' would have to appear twice on the wire, locally and
+# indirectly for the grandparent base; the collision doesn't care that
+# one instance is optional.
 { 'struct': 'Base',
   'data': { 'name': 'str' } }
 { 'struct': 'Mid',
diff --git a/tests/qapi-schema/struct-base-clash.err b/tests/qapi-schema/struct-base-clash.err
index 3ac37fb..3a9f66b 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:4: Member name 'name' clashes with base 'Base'
+tests/qapi-schema/struct-base-clash.json:5: Member name 'name' clashes with base 'Base'
diff --git a/tests/qapi-schema/struct-base-clash.json b/tests/qapi-schema/struct-base-clash.json
index f2afc9b..11aec80 100644
--- a/tests/qapi-schema/struct-base-clash.json
+++ b/tests/qapi-schema/struct-base-clash.json
@@ -1,4 +1,5 @@
-# we check for no duplicate keys with base
+# Reject attempts to duplicate QMP members
+# Here, 'name' would have to appear twice on the wire, locally and for base.
 { 'struct': 'Base',
   'data': { 'name': 'str' } }
 { 'struct': 'Sub',
diff --git a/tests/qapi-schema/union-clash-branches.err b/tests/qapi-schema/union-clash-branches.err
new file mode 100644
index 0000000..005c48d
--- /dev/null
+++ b/tests/qapi-schema/union-clash-branches.err
@@ -0,0 +1 @@
+tests/qapi-schema/union-clash-branches.json:4: Union 'TestUnion' member 'a_b' clashes with 'a-b'
diff --git a/tests/qapi-schema/union-clash-branches.exit b/tests/qapi-schema/union-clash-branches.exit
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/tests/qapi-schema/union-clash-branches.exit
@@ -0,0 +1 @@
+1
diff --git a/tests/qapi-schema/union-clash-branches.json b/tests/qapi-schema/union-clash-branches.json
new file mode 100644
index 0000000..31d135f
--- /dev/null
+++ b/tests/qapi-schema/union-clash-branches.json
@@ -0,0 +1,5 @@
+# Union branch name collision
+# Reject a union that would result in a collision in generated C names (this
+# would try to generate two enum values 'TEST_UNION_KIND_A_B').
+{ 'union': 'TestUnion',
+  'data': { 'a-b': 'int', 'a_b': 'str' } }
diff --git a/tests/qapi-schema/union-clash-branches.out b/tests/qapi-schema/union-clash-branches.out
new file mode 100644
index 0000000..e69de29
diff --git a/tests/qapi-schema/union-clash-data.err b/tests/qapi-schema/union-clash-data.err
new file mode 100644
index 0000000..e69de29
diff --git a/tests/qapi-schema/union-clash-data.exit b/tests/qapi-schema/union-clash-data.exit
new file mode 100644
index 0000000..573541a
--- /dev/null
+++ b/tests/qapi-schema/union-clash-data.exit
@@ -0,0 +1 @@
+0
diff --git a/tests/qapi-schema/union-clash-data.json b/tests/qapi-schema/union-clash-data.json
new file mode 100644
index 0000000..7308e69
--- /dev/null
+++ b/tests/qapi-schema/union-clash-data.json
@@ -0,0 +1,7 @@
+# Union branch 'data'
+# FIXME: this parses, but then fails to compile due to a duplicate 'data'
+# (one from the branch name, another as a filler to avoid an empty union).
+# we should either detect the collision at parse time, or change the
+# generated struct to allow this to compile.
+{ 'union': 'TestUnion',
+  'data': { 'data': 'int' } }
diff --git a/tests/qapi-schema/union-clash-data.out b/tests/qapi-schema/union-clash-data.out
new file mode 100644
index 0000000..6277239
--- /dev/null
+++ b/tests/qapi-schema/union-clash-data.out
@@ -0,0 +1,6 @@
+object :empty
+object :obj-int-wrapper
+    member data: int optional=False
+object TestUnion
+    case data: :obj-int-wrapper
+enum TestUnionKind ['data']
diff --git a/tests/qapi-schema/union-clash-type.err b/tests/qapi-schema/union-clash-type.err
new file mode 100644
index 0000000..6e64d1d
--- /dev/null
+++ b/tests/qapi-schema/union-clash-type.err
@@ -0,0 +1,16 @@
+Traceback (most recent call last):
+  File "tests/qapi-schema/test-qapi.py", line 55, in <module>
+    schema = QAPISchema(sys.argv[1])
+  File "scripts/qapi.py", line 1116, in __init__
+    self.check()
+  File "scripts/qapi.py", line 1299, in check
+    ent.check(self)
+  File "scripts/qapi.py", line 962, in check
+    self.variants.check(schema, members, seen)
+  File "scripts/qapi.py", line 1024, in check
+    v.check(schema, self.tag_member.type, vseen)
+  File "scripts/qapi.py", line 1032, in check
+    QAPISchemaObjectTypeMember.check(self, schema, [], seen)
+  File "scripts/qapi.py", line 994, in check
+    assert self.name not in seen
+AssertionError
diff --git a/tests/qapi-schema/union-clash-type.exit b/tests/qapi-schema/union-clash-type.exit
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/tests/qapi-schema/union-clash-type.exit
@@ -0,0 +1 @@
+1
diff --git a/tests/qapi-schema/union-clash-type.json b/tests/qapi-schema/union-clash-type.json
new file mode 100644
index 0000000..52c21f7
--- /dev/null
+++ b/tests/qapi-schema/union-clash-type.json
@@ -0,0 +1,10 @@
+# Union branch 'type'
+# FIXME: this triggers an assertion failure. But even with that fixed,
+# we would have a clash in generated C, between the simple union's
+# implicit tag member 'kind' and the branch name 'kind' within the
+# union. We should either reject this, or munge the generated C to let
+# it compile.
+# TODO: Even when the generated C is switched to use 'type' rather than
+# 'kind', to match the QMP spelling, the collision should still be detected.
+{ 'union': 'TestUnion',
+  'data': { 'kind': 'int', 'type': 'str' } }
