diff --git a/src/decoration_p.h b/src/decoration_p.h
--- a/src/decoration_p.h
+++ b/src/decoration_p.h
@@ -42,7 +42,7 @@
 class DecorationSettings;
 class DecorationShadow;
 
-class Decoration::Private
+class Q_DECL_HIDDEN Decoration::Private
 {
 public:
     Private(Decoration *decoration, const QVariantList &args);
diff --git a/src/decorationbutton_p.h b/src/decorationbutton_p.h
--- a/src/decorationbutton_p.h
+++ b/src/decorationbutton_p.h
@@ -39,7 +39,7 @@
 namespace KDecoration2
 {
 
-class DecorationButton::Private
+class Q_DECL_HIDDEN DecorationButton::Private
 {
 public:
     explicit Private(DecorationButtonType type, const QPointer<Decoration> &decoration, DecorationButton *parent);
diff --git a/src/decorationbuttongroup_p.h b/src/decorationbuttongroup_p.h
--- a/src/decorationbuttongroup_p.h
+++ b/src/decorationbuttongroup_p.h
@@ -40,7 +40,7 @@
 
 class Decoration;
 
-class DecorationButtonGroup::Private
+class Q_DECL_HIDDEN DecorationButtonGroup::Private
 {
 public:
     explicit Private(Decoration *decoration, DecorationButtonGroup *parent);
diff --git a/src/decorationshadow_p.h b/src/decorationshadow_p.h
--- a/src/decorationshadow_p.h
+++ b/src/decorationshadow_p.h
@@ -38,7 +38,7 @@
 namespace KDecoration2
 {
 
-class DecorationShadow::Private
+class Q_DECL_HIDDEN DecorationShadow::Private
 {
 public:
     explicit Private(DecorationShadow *parent);
diff --git a/src/private/decoratedclientprivate.cpp b/src/private/decoratedclientprivate.cpp
--- a/src/private/decoratedclientprivate.cpp
+++ b/src/private/decoratedclientprivate.cpp
@@ -24,7 +24,7 @@
 namespace KDecoration2
 {
 
-class DecoratedClientPrivate::Private
+class Q_DECL_HIDDEN DecoratedClientPrivate::Private
 {
 public:
     explicit Private(DecoratedClient *client, Decoration *decoration);
diff --git a/src/private/decorationsettingsprivate.cpp b/src/private/decorationsettingsprivate.cpp
--- a/src/private/decorationsettingsprivate.cpp
+++ b/src/private/decorationsettingsprivate.cpp
@@ -23,7 +23,7 @@
 namespace KDecoration2
 {
 
-class DecorationSettingsPrivate::Private
+class Q_DECL_HIDDEN DecorationSettingsPrivate::Private
 {
 public:
     explicit Private(DecorationSettings *settings);