diff --git a/src/lib/caching/kshareddatacache.cpp b/src/lib/caching/kshareddatacache.cpp
--- a/src/lib/caching/kshareddatacache.cpp
+++ b/src/lib/caching/kshareddatacache.cpp
@@ -970,7 +970,7 @@
 
 // The per-instance private data, such as map size, whether
 // attached or not, pointer to shared memory, etc.
-class KSharedDataCache::Private
+class Q_DECL_HIDDEN KSharedDataCache::Private
 {
 public:
     Private(const QString &name,
diff --git a/src/lib/caching/kshareddatacache_win.cpp b/src/lib/caching/kshareddatacache_win.cpp
--- a/src/lib/caching/kshareddatacache_win.cpp
+++ b/src/lib/caching/kshareddatacache_win.cpp
@@ -28,7 +28,7 @@
 #include <QtCore/QByteArray>
 #include <QtCore/QCache>
 
-class KSharedDataCache::Private
+class Q_DECL_HIDDEN KSharedDataCache::Private
 {
 public:
     KSharedDataCache::EvictionPolicy evictionPolicy;
diff --git a/src/lib/jobs/kjobtrackerinterface.cpp b/src/lib/jobs/kjobtrackerinterface.cpp
--- a/src/lib/jobs/kjobtrackerinterface.cpp
+++ b/src/lib/jobs/kjobtrackerinterface.cpp
@@ -21,7 +21,7 @@
 
 #include "kjob.h"
 
-class KJobTrackerInterface::Private
+class Q_DECL_HIDDEN KJobTrackerInterface::Private
 {
 public:
     Private(KJobTrackerInterface *interface) : q(interface)
diff --git a/src/lib/jobs/kjobuidelegate.cpp b/src/lib/jobs/kjobuidelegate.cpp
--- a/src/lib/jobs/kjobuidelegate.cpp
+++ b/src/lib/jobs/kjobuidelegate.cpp
@@ -22,7 +22,7 @@
 #include "kjobuidelegate.h"
 #include "kjob.h"
 
-class KJobUiDelegate::Private
+class Q_DECL_HIDDEN KJobUiDelegate::Private
 {
 public:
     Private(KJobUiDelegate *delegate)
diff --git a/src/lib/kaboutdata.cpp b/src/lib/kaboutdata.cpp
--- a/src/lib/kaboutdata.cpp
+++ b/src/lib/kaboutdata.cpp
@@ -48,7 +48,7 @@
 Q_LOGGING_CATEGORY(KABOUTDATA, "kf5.kcoreaddons.kaboutdata", QtWarningMsg)
 
 
-class KAboutPerson::Private
+class Q_DECL_HIDDEN KAboutPerson::Private
 {
 public:
     QString _name;
@@ -131,7 +131,7 @@
 }
 
 
-class KAboutLicense::Private : public QSharedData
+class Q_DECL_HIDDEN KAboutLicense::Private : public QSharedData
 {
 public:
     Private(LicenseKey licenseType,
@@ -438,7 +438,7 @@
     return KAboutLicense(license, restriction, nullptr);
 }
 
-class KAboutData::Private
+class Q_DECL_HIDDEN KAboutData::Private
 {
 public:
     Private()
diff --git a/src/lib/randomness/krandomsequence.cpp b/src/lib/randomness/krandomsequence.cpp
--- a/src/lib/randomness/krandomsequence.cpp
+++ b/src/lib/randomness/krandomsequence.cpp
@@ -21,7 +21,7 @@
 #include "krandomsequence.h"
 #include "krandom.h"
 
-class KRandomSequence::Private
+class Q_DECL_HIDDEN KRandomSequence::Private
 {
 public:
     enum {SHUFFLE_TABLE_SIZE = 32};
diff --git a/src/lib/util/kdelibs4configmigrator.cpp b/src/lib/util/kdelibs4configmigrator.cpp
--- a/src/lib/util/kdelibs4configmigrator.cpp
+++ b/src/lib/util/kdelibs4configmigrator.cpp
@@ -32,7 +32,7 @@
 // logging category for this framework, default: log stuff >= warning
 Q_LOGGING_CATEGORY(MIGRATOR, "kf5.kcoreaddons.kdelibs4configmigrator", QtWarningMsg)
 
-class Kdelibs4ConfigMigrator::Private
+class Q_DECL_HIDDEN Kdelibs4ConfigMigrator::Private
 {
 public:
     Private(const QString &_appName)
diff --git a/src/lib/util/kuser_unix.cpp b/src/lib/util/kuser_unix.cpp
--- a/src/lib/util/kuser_unix.cpp
+++ b/src/lib/util/kuser_unix.cpp
@@ -44,7 +44,7 @@
 static inline void endgrent() { }
 #endif
 
-class KUser::Private : public QSharedData
+class Q_DECL_HIDDEN KUser::Private : public QSharedData
 {
 public:
     uid_t uid;
@@ -336,7 +336,7 @@
 {
 }
 
-class KUserGroup::Private : public QSharedData
+class Q_DECL_HIDDEN KUserGroup::Private : public QSharedData
 {
 public:
     gid_t gid;
diff --git a/src/lib/util/kuser_win.cpp b/src/lib/util/kuser_win.cpp
--- a/src/lib/util/kuser_win.cpp
+++ b/src/lib/util/kuser_win.cpp
@@ -172,7 +172,7 @@
     });
 }
 
-class KUser::Private : public QSharedData
+class Q_DECL_HIDDEN KUser::Private : public QSharedData
 {
     typedef QExplicitlySharedDataPointer<Private> Ptr;
     Private() : isAdmin(false) {}
@@ -486,7 +486,7 @@
 {
 }
 
-class KUserGroup::Private : public QSharedData
+class Q_DECL_HIDDEN KUserGroup::Private : public QSharedData
 {
 public:
     QString name;