diff --git a/libtaskmanager/activityinfo.cpp b/libtaskmanager/activityinfo.cpp
index ebc1c2604..992f3e0b9 100644
--- a/libtaskmanager/activityinfo.cpp
+++ b/libtaskmanager/activityinfo.cpp
@@ -26,7 +26,7 @@ License along with this library.  If not, see <http://www.gnu.org/licenses/>.
 namespace TaskManager
 {
 
-class ActivityInfo::Private
+class Q_DECL_HIDDEN ActivityInfo::Private
 {
 public:
     Private(ActivityInfo *q);
diff --git a/libtaskmanager/flattentaskgroupsproxymodel.cpp b/libtaskmanager/flattentaskgroupsproxymodel.cpp
index 26ac99670..4a361050c 100644
--- a/libtaskmanager/flattentaskgroupsproxymodel.cpp
+++ b/libtaskmanager/flattentaskgroupsproxymodel.cpp
@@ -23,7 +23,7 @@ License along with this library.  If not, see <http://www.gnu.org/licenses/>.
 namespace TaskManager
 {
 
-class FlattenTaskGroupsProxyModel::Private
+class Q_DECL_HIDDEN FlattenTaskGroupsProxyModel::Private
 {
 public:
     Private(FlattenTaskGroupsProxyModel *q);
diff --git a/libtaskmanager/launchertasksmodel.cpp b/libtaskmanager/launchertasksmodel.cpp
index e216fb194..6aa264fee 100644
--- a/libtaskmanager/launchertasksmodel.cpp
+++ b/libtaskmanager/launchertasksmodel.cpp
@@ -55,7 +55,7 @@ inline bool isOnAllActivities(const ActivitiesCollection &activities)
 }
 
 
-class LauncherTasksModel::Private
+class Q_DECL_HIDDEN LauncherTasksModel::Private
 {
 public:
     Private(LauncherTasksModel *q);
diff --git a/libtaskmanager/startuptasksmodel.cpp b/libtaskmanager/startuptasksmodel.cpp
index f81be245d..595ad7c43 100644
--- a/libtaskmanager/startuptasksmodel.cpp
+++ b/libtaskmanager/startuptasksmodel.cpp
@@ -34,7 +34,7 @@ License along with this library.  If not, see <http://www.gnu.org/licenses/>.
 namespace TaskManager
 {
 
-class StartupTasksModel::Private
+class Q_DECL_HIDDEN StartupTasksModel::Private
 {
 public:
     Private(StartupTasksModel *q);
diff --git a/libtaskmanager/taskfilterproxymodel.cpp b/libtaskmanager/taskfilterproxymodel.cpp
index 9a28720da..8ebbab0d3 100644
--- a/libtaskmanager/taskfilterproxymodel.cpp
+++ b/libtaskmanager/taskfilterproxymodel.cpp
@@ -26,7 +26,7 @@ License along with this library.  If not, see <http://www.gnu.org/licenses/>.
 namespace TaskManager
 {
 
-class TaskFilterProxyModel::Private
+class Q_DECL_HIDDEN TaskFilterProxyModel::Private
 {
 public:
     Private(TaskFilterProxyModel *q);
diff --git a/libtaskmanager/taskgroupingproxymodel.cpp b/libtaskmanager/taskgroupingproxymodel.cpp
index bcad638ef..f787b625f 100644
--- a/libtaskmanager/taskgroupingproxymodel.cpp
+++ b/libtaskmanager/taskgroupingproxymodel.cpp
@@ -27,7 +27,7 @@ License along with this library.  If not, see <http://www.gnu.org/licenses/>.
 namespace TaskManager
 {
 
-class TaskGroupingProxyModel::Private
+class Q_DECL_HIDDEN TaskGroupingProxyModel::Private
 {
 public:
     Private(TaskGroupingProxyModel *q);
diff --git a/libtaskmanager/tasksmodel.cpp b/libtaskmanager/tasksmodel.cpp
index 8be6ffb35..e328a7408 100644
--- a/libtaskmanager/tasksmodel.cpp
+++ b/libtaskmanager/tasksmodel.cpp
@@ -41,7 +41,7 @@ License along with this library.  If not, see <http://www.gnu.org/licenses/>.
 namespace TaskManager
 {
 
-class TasksModel::Private
+class Q_DECL_HIDDEN TasksModel::Private
 {
 public:
     Private(TasksModel *q);
diff --git a/libtaskmanager/waylandtasksmodel.cpp b/libtaskmanager/waylandtasksmodel.cpp
index bcec6631f..73c3d6e66 100644
--- a/libtaskmanager/waylandtasksmodel.cpp
+++ b/libtaskmanager/waylandtasksmodel.cpp
@@ -42,7 +42,7 @@ License along with this library.  If not, see <http://www.gnu.org/licenses/>.
 namespace TaskManager
 {
 
-class WaylandTasksModel::Private
+class Q_DECL_HIDDEN WaylandTasksModel::Private
 {
 public:
     Private(WaylandTasksModel *q);
diff --git a/libtaskmanager/windowtasksmodel.cpp b/libtaskmanager/windowtasksmodel.cpp
index 509d35856..663f58607 100644
--- a/libtaskmanager/windowtasksmodel.cpp
+++ b/libtaskmanager/windowtasksmodel.cpp
@@ -32,7 +32,7 @@ License along with this library.  If not, see <http://www.gnu.org/licenses/>.
 namespace TaskManager
 {
 
-class WindowTasksModel::Private
+class Q_DECL_HIDDEN WindowTasksModel::Private
 {
 public:
     Private(WindowTasksModel *q);
diff --git a/libtaskmanager/xwindowtasksmodel.cpp b/libtaskmanager/xwindowtasksmodel.cpp
index 349faae93..2e0614283 100644
--- a/libtaskmanager/xwindowtasksmodel.cpp
+++ b/libtaskmanager/xwindowtasksmodel.cpp
@@ -50,7 +50,7 @@ static const NET::Properties windowInfoFlags = NET::WMState | NET::XAWMState | N
 static const NET::Properties2 windowInfoFlags2 = NET::WM2DesktopFileName | NET::WM2Activities |
     NET::WM2WindowClass | NET::WM2AllowedActions;
 
-class XWindowTasksModel::Private
+class Q_DECL_HIDDEN XWindowTasksModel::Private
 {
 public:
     Private(XWindowTasksModel *q);