diff --git a/qapi/machine.json b/qapi/machine.json
index 2df407e877..3e9cc3f17d 100644
--- a/qapi/machine.json
+++ b/qapi/machine.json
@@ -135,6 +135,26 @@
 ##
 { 'command': 'query-cpus-fast', 'returns': [ 'CpuInfoFast' ] }
 
+##
+# @CompatProperty:
+#
+# Property default values specific to a machine type, for use by
+# scripts/compare-machine-types.
+#
+# @qom-type: name of the QOM type to which the default applies
+#
+# @property: name of its property to which the default applies
+#
+# @value: the default value (machine-specific default can overwrite
+#     the "default" default, to avoid this use -machine none)
+#
+# Since: 9.1
+##
+{ 'struct': 'CompatProperty',
+  'data': { 'qom-type': 'str',
+            'property': 'str',
+            'value': 'str' } }
+
 ##
 # @MachineInfo:
 #
@@ -166,6 +186,14 @@
 #
 # @acpi: machine type supports ACPI (since 8.0)
 #
+# @compat-props: The machine type's compatibility properties.  Only
+#     present when query-machines argument @compat-props is true.
+#     (since 9.1)
+#
+# Features:
+#
+# @unstable: Member @compat-props is experimental.
+#
 # Since: 1.2
 ##
 { 'struct': 'MachineInfo',
@@ -173,18 +201,53 @@
             '*is-default': 'bool', 'cpu-max': 'int',
             'hotpluggable-cpus': 'bool',  'numa-mem-supported': 'bool',
             'deprecated': 'bool', '*default-cpu-type': 'str',
-            '*default-ram-id': 'str', 'acpi': 'bool' } }
+            '*default-ram-id': 'str', 'acpi': 'bool',
+            '*compat-props': { 'type': ['CompatProperty'],
+                               'features': ['unstable'] } } }
 
 ##
 # @query-machines:
 #
 # Return a list of supported machines
 #
+# @compat-props: if true, also return compatibility properties.
+#     (default: false) (since 9.1)
+#
+# Features:
+#
+# @unstable: Argument @compat-props is experimental.
+#
 # Returns: a list of MachineInfo
 #
 # Since: 1.2
+#
+# Example:
+#
+#     -> { "execute": "query-machines", "arguments": { "compat-props": true } }
+#     <- { "return": [
+#               {
+#                  "hotpluggable-cpus": true,
+#                  "name": "pc-q35-6.2",
+#                  "compat-props": [
+#                       {
+#                          "qom-type": "virtio-mem",
+#                          "property": "unplugged-inaccessible",
+#                          "value": "off"
+#                       }
+#                   ],
+#                   "numa-mem-supported": false,
+#                   "default-cpu-type": "qemu64-x86_64-cpu",
+#                   "cpu-max": 288,
+#                   "deprecated": false,
+#                   "default-ram-id": "pc.ram"
+#               },
+#               ...
+#        }
 ##
-{ 'command': 'query-machines', 'returns': ['MachineInfo'] }
+{ 'command': 'query-machines',
+  'data': { '*compat-props': { 'type': 'bool',
+                               'features': [ 'unstable' ] } },
+  'returns': ['MachineInfo'] }
 
 ##
 # @CurrentMachineParams:
diff --git a/hw/core/machine-qmp-cmds.c b/hw/core/machine-qmp-cmds.c
index c20829b9ae..5972100b1f 100644
--- a/hw/core/machine-qmp-cmds.c
+++ b/hw/core/machine-qmp-cmds.c
@@ -64,7 +64,8 @@ CpuInfoFastList *qmp_query_cpus_fast(Error **errp)
     return head;
 }
 
-MachineInfoList *qmp_query_machines(Error **errp)
+MachineInfoList *qmp_query_machines(bool has_compat_props, bool compat_props,
+                                    Error **errp)
 {
     GSList *el, *machines = object_class_get_list(TYPE_MACHINE, false);
     MachineInfoList *mach_list = NULL;
@@ -96,6 +97,26 @@ MachineInfoList *qmp_query_machines(Error **errp)
             info->default_ram_id = g_strdup(mc->default_ram_id);
         }
 
+        if (compat_props && mc->compat_props) {
+            int i;
+            info->compat_props = NULL;
+            CompatPropertyList **tail = &(info->compat_props);
+            info->has_compat_props = true;
+
+            for (i = 0; i < mc->compat_props->len; i++) {
+                GlobalProperty *mt_prop = g_ptr_array_index(mc->compat_props,
+                                                            i);
+                CompatProperty *prop;
+
+                prop = g_malloc0(sizeof(*prop));
+                prop->qom_type = g_strdup(mt_prop->driver);
+                prop->property = g_strdup(mt_prop->property);
+                prop->value = g_strdup(mt_prop->value);
+
+                QAPI_LIST_APPEND(tail, prop);
+            }
+        }
+
         QAPI_LIST_PREPEND(mach_list, info);
     }
 
diff --git a/tests/qtest/fuzz/qos_fuzz.c b/tests/qtest/fuzz/qos_fuzz.c
index e403d373a0..b71e945c5f 100644
--- a/tests/qtest/fuzz/qos_fuzz.c
+++ b/tests/qtest/fuzz/qos_fuzz.c
@@ -46,7 +46,7 @@ static void qos_set_machines_devices_available(void)
     MachineInfoList *mach_info;
     ObjectTypeInfoList *type_info;
 
-    mach_info = qmp_query_machines(&error_abort);
+    mach_info = qmp_query_machines(false, false, &error_abort);
     machines_apply_to_node(mach_info);
     qapi_free_MachineInfoList(mach_info);
 
