diff --git a/scripts/qapi/expr.py b/scripts/qapi/expr.py
index c0d18dcc01..03624bdf3f 100644
--- a/scripts/qapi/expr.py
+++ b/scripts/qapi/expr.py
@@ -283,6 +283,9 @@ def check_union(expr, info):
             raise QAPISemError(info, "'discriminator' requires 'base'")
         check_name_is_str(discriminator, info, "'discriminator'")
 
+    if not isinstance(members, dict):
+        raise QAPISemError(info, "'data' must be an object")
+
     for (key, value) in members.items():
         source = "'data' member '%s'" % key
         if discriminator is None:
@@ -298,6 +301,10 @@ def check_alternate(expr, info):
 
     if not members:
         raise QAPISemError(info, "'data' must not be empty")
+
+    if not isinstance(members, dict):
+        raise QAPISemError(info, "'data' must be an object")
+
     for (key, value) in members.items():
         source = "'data' member '%s'" % key
         check_name_lower(key, info, source)
diff --git a/tests/qapi-schema/alternate-data-invalid.err b/tests/qapi-schema/alternate-data-invalid.err
new file mode 100644
index 0000000000..55f1033aef
--- /dev/null
+++ b/tests/qapi-schema/alternate-data-invalid.err
@@ -0,0 +1,2 @@
+alternate-data-invalid.json: In alternate 'Alt':
+alternate-data-invalid.json:2: 'data' must be an object
diff --git a/tests/qapi-schema/alternate-data-invalid.json b/tests/qapi-schema/alternate-data-invalid.json
new file mode 100644
index 0000000000..7d5d905581
--- /dev/null
+++ b/tests/qapi-schema/alternate-data-invalid.json
@@ -0,0 +1,4 @@
+# Alternate type requires an object for 'data'
+{ 'alternate': 'Alt',
+  'data': ['rubbish', 'nonsense']
+}
diff --git a/tests/qapi-schema/alternate-data-invalid.out b/tests/qapi-schema/alternate-data-invalid.out
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/tests/qapi-schema/meson.build b/tests/qapi-schema/meson.build
index 8ba6917132..d7163e6601 100644
--- a/tests/qapi-schema/meson.build
+++ b/tests/qapi-schema/meson.build
@@ -14,6 +14,7 @@ schemas = [
   'alternate-conflict-string.json',
   'alternate-conflict-bool-string.json',
   'alternate-conflict-num-string.json',
+  'alternate-data-invalid.json',
   'alternate-empty.json',
   'alternate-invalid-dict.json',
   'alternate-nested.json',
@@ -192,6 +193,7 @@ schemas = [
   'union-clash-branches.json',
   'union-empty.json',
   'union-invalid-base.json',
+  'union-invalid-data.json',
   'union-optional-branch.json',
   'union-unknown.json',
   'unknown-escape.json',
diff --git a/tests/qapi-schema/union-invalid-data.err b/tests/qapi-schema/union-invalid-data.err
new file mode 100644
index 0000000000..e26cf769a3
--- /dev/null
+++ b/tests/qapi-schema/union-invalid-data.err
@@ -0,0 +1,2 @@
+union-invalid-data.json: In union 'TestUnion':
+union-invalid-data.json:2: 'data' must be an object
diff --git a/tests/qapi-schema/union-invalid-data.json b/tests/qapi-schema/union-invalid-data.json
new file mode 100644
index 0000000000..395ba24d39
--- /dev/null
+++ b/tests/qapi-schema/union-invalid-data.json
@@ -0,0 +1,6 @@
+# the union data type must be an object.
+{ 'union': 'TestUnion',
+  'base': 'int',
+  'discriminator': 'int',
+  'data': ['rubbish', 'nonsense']
+}
diff --git a/tests/qapi-schema/union-invalid-data.out b/tests/qapi-schema/union-invalid-data.out
new file mode 100644
index 0000000000..e69de29bb2