diff --git a/src/libnm-core-impl/nm-setting-bridge.c b/src/libnm-core-impl/nm-setting-bridge.c
index 2624a4e3e3..4567a28f0a 100644
--- a/src/libnm-core-impl/nm-setting-bridge.c
+++ b/src/libnm-core-impl/nm-setting-bridge.c
@@ -1564,19 +1564,13 @@ nm_setting_bridge_init(NMSettingBridge *setting)
     priv->multicast_last_member_interval    = NM_BRIDGE_MULTICAST_LAST_MEMBER_INTERVAL_DEF;
     priv->multicast_membership_interval     = NM_BRIDGE_MULTICAST_MEMBERSHIP_INTERVAL_DEF;
     priv->multicast_hash_max                = NM_BRIDGE_MULTICAST_HASH_MAX_DEF;
-    priv->multicast_snooping                = NM_BRIDGE_MULTICAST_SNOOPING_DEF;
     priv->priority                          = NM_BRIDGE_PRIORITY_DEF;
-    priv->stp                               = NM_BRIDGE_STP_DEF;
     priv->vlan_default_pvid                 = NM_BRIDGE_VLAN_DEFAULT_PVID_DEF;
     priv->multicast_query_interval          = NM_BRIDGE_MULTICAST_QUERY_INTERVAL_DEF;
     priv->multicast_query_response_interval = NM_BRIDGE_MULTICAST_QUERY_RESPONSE_INTERVAL_DEF;
     priv->multicast_querier_interval        = NM_BRIDGE_MULTICAST_QUERIER_INTERVAL_DEF;
     priv->multicast_startup_query_count     = NM_BRIDGE_MULTICAST_STARTUP_QUERY_COUNT_DEF;
     priv->multicast_startup_query_interval  = NM_BRIDGE_MULTICAST_STARTUP_QUERY_INTERVAL_DEF;
-
-    nm_assert(priv->multicast_querier == NM_BRIDGE_MULTICAST_QUERIER_DEF);
-    nm_assert(priv->multicast_query_use_ifaddr == NM_BRIDGE_MULTICAST_QUERY_USE_IFADDR_DEF);
-    nm_assert(priv->vlan_stats_enabled == NM_BRIDGE_VLAN_STATS_ENABLED_DEF);
 }
 
 /**
diff --git a/src/libnm-core-impl/nm-setting-connection.c b/src/libnm-core-impl/nm-setting-connection.c
index a044f1ae21..869093f156 100644
--- a/src/libnm-core-impl/nm-setting-connection.c
+++ b/src/libnm-core-impl/nm-setting-connection.c
@@ -1801,7 +1801,6 @@ nm_setting_connection_init(NMSettingConnection *setting)
     NMSettingConnectionPrivate *priv = NM_SETTING_CONNECTION_GET_PRIVATE(setting);
 
     priv->auth_retries         = -1;
-    priv->autoconnect          = TRUE;
     priv->autoconnect_priority = NM_SETTING_CONNECTION_AUTOCONNECT_PRIORITY_DEFAULT;
     priv->autoconnect_retries  = -1;
     priv->autoconnect_slaves   = NM_SETTING_CONNECTION_AUTOCONNECT_SLAVES_DEFAULT;
diff --git a/src/libnm-core-impl/nm-setting-ip-config.c b/src/libnm-core-impl/nm-setting-ip-config.c
index a9214af4e4..f1e0d7adce 100644
--- a/src/libnm-core-impl/nm-setting-ip-config.c
+++ b/src/libnm-core-impl/nm-setting-ip-config.c
@@ -6063,15 +6063,13 @@ _nm_setting_ip_config_private_init(gpointer self, NMSettingIPConfigPrivate *priv
 {
     nm_assert(NM_IS_SETTING_IP_CONFIG(self));
 
-    priv->dns                = g_ptr_array_new_with_free_func(g_free);
-    priv->dns_search         = g_ptr_array_new_with_free_func(g_free);
-    priv->addresses          = g_ptr_array_new_with_free_func((GDestroyNotify) nm_ip_address_unref);
-    priv->routes             = g_ptr_array_new_with_free_func((GDestroyNotify) nm_ip_route_unref);
-    priv->route_metric       = -1;
-    priv->dhcp_send_hostname = TRUE;
-    priv->may_fail           = TRUE;
-    priv->dad_timeout        = -1;
-    priv->required_timeout   = -1;
+    priv->dns              = g_ptr_array_new_with_free_func(g_free);
+    priv->dns_search       = g_ptr_array_new_with_free_func(g_free);
+    priv->addresses        = g_ptr_array_new_with_free_func((GDestroyNotify) nm_ip_address_unref);
+    priv->routes           = g_ptr_array_new_with_free_func((GDestroyNotify) nm_ip_route_unref);
+    priv->route_metric     = -1;
+    priv->dad_timeout      = -1;
+    priv->required_timeout = -1;
 }
 
 static void
diff --git a/src/libnm-core-impl/nm-setting-ip-tunnel.c b/src/libnm-core-impl/nm-setting-ip-tunnel.c
index 66a2cb551b..f75ca1d5b7 100644
--- a/src/libnm-core-impl/nm-setting-ip-tunnel.c
+++ b/src/libnm-core-impl/nm-setting-ip-tunnel.c
@@ -615,11 +615,7 @@ set_property(GObject *object, guint prop_id, const GValue *value, GParamSpec *ps
 
 static void
 nm_setting_ip_tunnel_init(NMSettingIPTunnel *self)
-{
-    NMSettingIPTunnelPrivate *priv = NM_SETTING_IP_TUNNEL_GET_PRIVATE(self);
-
-    priv->path_mtu_discovery = TRUE;
-}
+{}
 
 /**
  * nm_setting_ip_tunnel_new:
diff --git a/src/libnm-core-impl/nm-setting-macsec.c b/src/libnm-core-impl/nm-setting-macsec.c
index 1802ba6d21..1a9e9bd8ab 100644
--- a/src/libnm-core-impl/nm-setting-macsec.c
+++ b/src/libnm-core-impl/nm-setting-macsec.c
@@ -492,9 +492,7 @@ nm_setting_macsec_init(NMSettingMacsec *self)
     NMSettingMacsecPrivate *priv = NM_SETTING_MACSEC_GET_PRIVATE(self);
 
     nm_assert(priv->mode == NM_SETTING_MACSEC_MODE_PSK);
-    priv->encrypt    = TRUE;
     priv->port       = 1;
-    priv->send_sci   = TRUE;
     priv->validation = NM_SETTING_MACSEC_VALIDATION_STRICT;
 }
 
diff --git a/src/libnm-core-impl/nm-setting-macvlan.c b/src/libnm-core-impl/nm-setting-macvlan.c
index 255ec7d595..32b30c2cfa 100644
--- a/src/libnm-core-impl/nm-setting-macvlan.c
+++ b/src/libnm-core-impl/nm-setting-macvlan.c
@@ -234,11 +234,7 @@ set_property(GObject *object, guint prop_id, const GValue *value, GParamSpec *ps
 
 static void
 nm_setting_macvlan_init(NMSettingMacvlan *self)
-{
-    NMSettingMacvlanPrivate *priv = NM_SETTING_MACVLAN_GET_PRIVATE(self);
-
-    priv->promiscuous = TRUE;
-}
+{}
 
 /**
  * nm_setting_macvlan_new:
diff --git a/src/libnm-core-impl/nm-setting-ppp.c b/src/libnm-core-impl/nm-setting-ppp.c
index 7e62ec6569..74bd2572d2 100644
--- a/src/libnm-core-impl/nm-setting-ppp.c
+++ b/src/libnm-core-impl/nm-setting-ppp.c
@@ -512,11 +512,7 @@ set_property(GObject *object, guint prop_id, const GValue *value, GParamSpec *ps
 
 static void
 nm_setting_ppp_init(NMSettingPpp *self)
-{
-    NMSettingPppPrivate *priv = NM_SETTING_PPP_GET_PRIVATE(self);
-
-    priv->noauth = TRUE;
-}
+{}
 
 /**
  * nm_setting_ppp_new:
diff --git a/src/libnm-core-impl/nm-setting-vxlan.c b/src/libnm-core-impl/nm-setting-vxlan.c
index e625034338..c2d23a7fb6 100644
--- a/src/libnm-core-impl/nm-setting-vxlan.c
+++ b/src/libnm-core-impl/nm-setting-vxlan.c
@@ -536,7 +536,6 @@ nm_setting_vxlan_init(NMSettingVxlan *self)
 
     priv->destination_port = DST_PORT_DEFAULT;
     priv->ageing           = 300;
-    priv->learning         = TRUE;
 }
 
 /**
diff --git a/src/libnm-core-impl/nm-setting-wireguard.c b/src/libnm-core-impl/nm-setting-wireguard.c
index d6fa853bed..a270881edf 100644
--- a/src/libnm-core-impl/nm-setting-wireguard.c
+++ b/src/libnm-core-impl/nm-setting-wireguard.c
@@ -2372,7 +2372,6 @@ nm_setting_wireguard_init(NMSettingWireGuard *setting)
 
     priv->peers_arr              = g_ptr_array_new();
     priv->peers_hash             = g_hash_table_new(nm_pstr_hash, nm_pstr_equal);
-    priv->peer_routes            = TRUE;
     priv->ip4_auto_default_route = NM_TERNARY_DEFAULT;
     priv->ip6_auto_default_route = NM_TERNARY_DEFAULT;
 }
diff --git a/src/libnm-core-impl/nm-setting.c b/src/libnm-core-impl/nm-setting.c
index a473dbc7ae..f81367097a 100644
--- a/src/libnm-core-impl/nm-setting.c
+++ b/src/libnm-core-impl/nm-setting.c
@@ -753,6 +753,59 @@ out_fail:
 
 /*****************************************************************************/
 
+static void
+_init_direct(NMSetting *setting)
+{
+    const NMSettInfoSetting *sett_info;
+    guint                    i;
+
+    sett_info = _nm_setting_class_get_sett_info(NM_SETTING_GET_CLASS(setting));
+    nm_assert(sett_info);
+
+    for (i = 0; i < sett_info->property_infos_len; i++) {
+        const NMSettInfoProperty *property_info = &sett_info->property_infos[i];
+
+        /* We don't emit any g_object_notify_by_pspec(), because this is
+         * only supposed to be called during initialization of the GObject
+         * instance. */
+
+        switch (property_info->property_type->direct_type) {
+        case NM_VALUE_TYPE_NONE:
+            break;
+        case NM_VALUE_TYPE_BOOL:
+        {
+            bool *p_val = _nm_setting_get_private(setting, sett_info, property_info->direct_offset);
+            gboolean def_val;
+
+            def_val = NM_G_PARAM_SPEC_GET_DEFAULT_BOOLEAN(property_info->param_spec);
+            nm_assert(*p_val == FALSE);
+            *p_val = def_val;
+            break;
+        }
+        case NM_VALUE_TYPE_UINT32:
+        {
+            guint32 *p_val =
+                _nm_setting_get_private(setting, sett_info, property_info->direct_offset);
+            guint def_val;
+
+            def_val = NM_G_PARAM_SPEC_GET_DEFAULT_UINT(property_info->param_spec);
+            nm_assert(*p_val == 0);
+            *p_val = def_val;
+            break;
+        }
+        case NM_VALUE_TYPE_STRING:
+            nm_assert(!NM_G_PARAM_SPEC_GET_DEFAULT_STRING(property_info->param_spec));
+            nm_assert(!(
+                *((const char *const *)
+                      _nm_setting_get_private(setting, sett_info, property_info->direct_offset))));
+            break;
+        default:
+            nm_assert_not_reached();
+            break;
+        }
+    }
+}
+
 static void
 _finalize_direct(NMSetting *setting)
 {
@@ -3129,6 +3182,32 @@ static void
 nm_setting_init(NMSetting *setting)
 {}
 
+static void
+constructed(GObject *object)
+{
+    NMSetting *     self  = NM_SETTING(object);
+    NMSettingClass *klass = NM_SETTING_GET_CLASS(self);
+
+    /* we don't support that NMSetting subclasses override constructed.
+     * They all must have no G_PARAM_CONSTRUCT/G_PARAM_CONSTRUCT_ONLY
+     * properties, otherwise the automatism of _init_direct() needs
+     * careful adjustment. */
+    nm_assert(G_OBJECT_CLASS(klass)->constructed == constructed);
+
+    /* we always initialize the defaults of the (direct) properties. Note that:
+     *
+     * - we don't use CONSTRUCT properties, because they have an overhead during
+     *   each object creation. Via _init_direct() we can do it more efficiently.
+     *
+     * - we always call this, because we want to get all default values right.
+     *   We even call this for NMSetting subclasses that (historically) are not
+     *   yet aware of this happening.
+     */
+    _init_direct(self);
+
+    G_OBJECT_CLASS(nm_setting_parent_class)->constructed(object);
+}
+
 static void
 finalize(GObject *object)
 {
@@ -3156,6 +3235,7 @@ nm_setting_class_init(NMSettingClass *setting_class)
 
     g_type_class_add_private(setting_class, sizeof(NMSettingPrivate));
 
+    object_class->constructed  = constructed;
     object_class->get_property = get_property;
     object_class->finalize     = finalize;
 
diff --git a/src/libnm-core-impl/tests/test-setting.c b/src/libnm-core-impl/tests/test-setting.c
index b0511ef9a4..51077e2360 100644
--- a/src/libnm-core-impl/tests/test-setting.c
+++ b/src/libnm-core-impl/tests/test-setting.c
@@ -4566,6 +4566,9 @@ check_done:;
 
                 if (NM_FLAGS_HAS(sip->param_spec->flags, NM_SETTING_PARAM_TO_DBUS_IGNORE_FLAGS))
                     g_assert(sip->property_type->to_dbus_fcn);
+
+                g_assert(!NM_FLAGS_HAS(sip->param_spec->flags, G_PARAM_CONSTRUCT));
+                g_assert(!NM_FLAGS_HAS(sip->param_spec->flags, G_PARAM_CONSTRUCT_ONLY));
             }
         }