diff --git a/pri/build_opts.pri b/pri/build_opts.pri
index 4a6d4b322..37c36a1be 100644
--- a/pri/build_opts.pri
+++ b/pri/build_opts.pri
@@ -4,6 +4,10 @@ DEFINES *= QT_USE_QSTRINGBUILDER QT_USE_FAST_CONCATENATION QT_USE_FAST_OPERATOR_
 VERSION = $$APP_VERSION
 QT *= core gui widgets sql network xml qml
 
+greaterThan(QT_MAJOR_VERSION, 5) {
+  QT*= core5compat
+}
+
 equals(USE_WEBENGINE, true) {
   message($$MSG_PREFIX: Application will be compiled WITH QtWebEngine module.)
   QT *= webenginewidgets
diff --git a/resources/desktop/com.github.rssguard.appdata.xml b/resources/desktop/com.github.rssguard.appdata.xml
index 55ad144e8..0a35f2810 100644
--- a/resources/desktop/com.github.rssguard.appdata.xml
+++ b/resources/desktop/com.github.rssguard.appdata.xml
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<!-- Copyright 2017-2019 Martin Rotter <rotter.martinos@gmail.com> -->
+<!-- Copyright 2017-2020 Martin Rotter <rotter.martinos@gmail.com> -->
 <component type="desktop-application">
   <id>com.github.rssguard.desktop</id>
   <metadata_license>CC0-1.0</metadata_license>
diff --git a/src/librssguard/3rd-party/mimesis/mimesis.cpp b/src/librssguard/3rd-party/mimesis/mimesis.cpp
index 81eb52813..c0cf25710 100755
--- a/src/librssguard/3rd-party/mimesis/mimesis.cpp
+++ b/src/librssguard/3rd-party/mimesis/mimesis.cpp
@@ -352,7 +352,7 @@ namespace Mimesis {
     return unquote(str.substr(start, end - start));
   }
 
-  static const string ending[2] = {"\n", "\r\n"};
+  static const string ending[2] = { "\n", "\r\n" };
 
   Part::Part() :
     headers(),
@@ -805,7 +805,7 @@ namespace Mimesis {
     QLocale loc("C");
     QDateTime dat;
 
-    dat.fromTime_t(date.time_since_epoch().count());
+    dat.setSecsSinceEpoch(date.time_since_epoch().count());
 
     return loc.toString(dat, "ddd, MM MMM yyyy HH:mm:ss t").toStdString();
 
diff --git a/src/librssguard/dynamic-shortcuts/dynamicshortcutswidget.cpp b/src/librssguard/dynamic-shortcuts/dynamicshortcutswidget.cpp
index 789de61c1..3409c612a 100644
--- a/src/librssguard/dynamic-shortcuts/dynamicshortcutswidget.cpp
+++ b/src/librssguard/dynamic-shortcuts/dynamicshortcutswidget.cpp
@@ -12,7 +12,11 @@
 DynamicShortcutsWidget::DynamicShortcutsWidget(QWidget* parent) : QWidget(parent) {
   // Create layout for this control and set is as active.
   m_layout = new QGridLayout(this);
+
+#if QT_VERSION_MAJOR <= 5
   m_layout->setMargin(0);
+#endif
+
   setLayout(m_layout);
 }
 
diff --git a/src/librssguard/dynamic-shortcuts/shortcutcatcher.cpp b/src/librssguard/dynamic-shortcuts/shortcutcatcher.cpp
index 5b903aa6d..e90cf1227 100644
--- a/src/librssguard/dynamic-shortcuts/shortcutcatcher.cpp
+++ b/src/librssguard/dynamic-shortcuts/shortcutcatcher.cpp
@@ -12,7 +12,11 @@ ShortcutCatcher::ShortcutCatcher(QWidget* parent)
   : QWidget(parent), m_isRecording(false), m_numKey(0), m_modifierKeys(0U) {
   // Setup layout of the control
   m_layout = new QHBoxLayout(this);
+
+#if QT_VERSION_MAJOR <= 5
   m_layout->setMargin(0);
+#endif
+
   m_layout->setSpacing(1);
 
   // Create reset button.
diff --git a/src/librssguard/gui/dialogs/formaddaccount.cpp b/src/librssguard/gui/dialogs/formaddaccount.cpp
index b7c53c703..372febd31 100644
--- a/src/librssguard/gui/dialogs/formaddaccount.cpp
+++ b/src/librssguard/gui/dialogs/formaddaccount.cpp
@@ -8,7 +8,6 @@
 #include "miscellaneous/iconfactory.h"
 #include "services/standard/standardserviceentrypoint.h"
 
-#include <QDesktopWidget>
 #include <QDialogButtonBox>
 #include <QListWidget>
 #include <QSize>
diff --git a/src/librssguard/gui/dialogs/formmain.cpp b/src/librssguard/gui/dialogs/formmain.cpp
index 93da546e9..0047bae30 100755
--- a/src/librssguard/gui/dialogs/formmain.cpp
+++ b/src/librssguard/gui/dialogs/formmain.cpp
@@ -39,7 +39,6 @@
 #endif
 
 #include <QCloseEvent>
-#include <QDesktopWidget>
 #include <QFileDialog>
 #include <QRect>
 #include <QScopedPointer>
diff --git a/src/librssguard/gui/feedmessageviewer.cpp b/src/librssguard/gui/feedmessageviewer.cpp
index 4ae294661..f82437929 100644
--- a/src/librssguard/gui/feedmessageviewer.cpp
+++ b/src/librssguard/gui/feedmessageviewer.cpp
@@ -259,11 +259,14 @@ void FeedMessageViewer::initializeViews() {
   auto* message_layout = new QVBoxLayout(m_messagesWidget);
 
   // Set layout properties.
+#if QT_VERSION_MAJOR <= 5
   central_layout->setMargin(0);
-  central_layout->setSpacing(0);
   feed_layout->setMargin(0);
-  feed_layout->setSpacing(0);
   message_layout->setMargin(0);
+#endif
+
+  central_layout->setSpacing(0);
+  feed_layout->setSpacing(0);
   message_layout->setSpacing(0);
 
   // Set views.
diff --git a/src/librssguard/gui/messagesview.cpp b/src/librssguard/gui/messagesview.cpp
index 3fd57948c..804c50b3f 100644
--- a/src/librssguard/gui/messagesview.cpp
+++ b/src/librssguard/gui/messagesview.cpp
@@ -568,7 +568,11 @@ void MessagesView::selectNextUnreadItem() {
 }
 
 void MessagesView::searchMessages(const QString& pattern) {
+#if QT_VERSION_MAJOR <= 5
   m_proxyModel->setFilterRegExp(pattern);
+#else
+  m_proxyModel->setFilterRegularExpression(pattern);
+#endif
 
   if (selectionModel()->selectedRows().isEmpty()) {
     emit currentMessageRemoved();
diff --git a/src/librssguard/gui/styleditemdelegatewithoutfocus.h b/src/librssguard/gui/styleditemdelegatewithoutfocus.h
index 81372ec32..f9d4a80b0 100644
--- a/src/librssguard/gui/styleditemdelegatewithoutfocus.h
+++ b/src/librssguard/gui/styleditemdelegatewithoutfocus.h
@@ -4,7 +4,12 @@
 #define STYLEDITEMDELEGATEWITHOUTFOCUS_H
 
 #include <QStyledItemDelegate>
+
+#if QT_VERSION_MAJOR <= 5
 #include <QStyleOptionViewItemV4>
+#else
+#include <QStyleOptionViewItem>
+#endif
 
 class StyledItemDelegateWithoutFocus : public QStyledItemDelegate {
   Q_OBJECT
diff --git a/src/librssguard/gui/widgetwithstatus.cpp b/src/librssguard/gui/widgetwithstatus.cpp
index 81817418c..48ea56626 100644
--- a/src/librssguard/gui/widgetwithstatus.cpp
+++ b/src/librssguard/gui/widgetwithstatus.cpp
@@ -19,7 +19,10 @@ WidgetWithStatus::WidgetWithStatus(QWidget* parent)
   m_iconOk = qApp->icons()->fromTheme(QSL("dialog-yes"));
 
   // Set layout properties.
+#if QT_VERSION_MAJOR <= 5
   m_layout->setMargin(0);
+#endif
+
   setLayout(m_layout);
   setStatus(StatusType::Information, QString());
 }
diff --git a/src/librssguard/miscellaneous/mutex.cpp b/src/librssguard/miscellaneous/mutex.cpp
index dda2beab5..76dd857e4 100644
--- a/src/librssguard/miscellaneous/mutex.cpp
+++ b/src/librssguard/miscellaneous/mutex.cpp
@@ -4,7 +4,7 @@
 
 #include "definitions/definitions.h"
 
-Mutex::Mutex(QMutex::RecursionMode mode, QObject* parent) : QObject(parent), m_mutex(new QMutex(mode)), m_isLocked(false) {}
+Mutex::Mutex(QObject* parent) : QObject(parent), m_mutex(new QMutex()), m_isLocked(false) {}
 
 Mutex::~Mutex() {
   qDebugNN << LOGSEC_CORE << ("Destroying Mutex instance.");
diff --git a/src/librssguard/miscellaneous/mutex.h b/src/librssguard/miscellaneous/mutex.h
index d9dce9f7a..544207d34 100644
--- a/src/librssguard/miscellaneous/mutex.h
+++ b/src/librssguard/miscellaneous/mutex.h
@@ -10,9 +10,7 @@ class Mutex : public QObject {
   Q_OBJECT
 
   public:
-
-    // Constructors.
-    explicit Mutex(QMutex::RecursionMode mode = QMutex::NonRecursive, QObject* parent = 0);
+    explicit Mutex(QObject* parent = nullptr);
     virtual ~Mutex();
 
     // Main methods.
diff --git a/src/librssguard/miscellaneous/simplecrypt/simplecrypt.cpp b/src/librssguard/miscellaneous/simplecrypt/simplecrypt.cpp
index 5dd1ea909..64d7d7341 100644
--- a/src/librssguard/miscellaneous/simplecrypt/simplecrypt.cpp
+++ b/src/librssguard/miscellaneous/simplecrypt/simplecrypt.cpp
@@ -31,6 +31,7 @@
 #include <QCryptographicHash>
 #include <QDataStream>
 #include <QDateTime>
+#include <QIODevice>
 #include <QRandomGenerator>
 #include <QtDebug>
 #include <QtGlobal>
diff --git a/src/librssguard/services/abstract/cacheforserviceroot.cpp b/src/librssguard/services/abstract/cacheforserviceroot.cpp
index eed3cbd70..f4cf57abe 100644
--- a/src/librssguard/services/abstract/cacheforserviceroot.cpp
+++ b/src/librssguard/services/abstract/cacheforserviceroot.cpp
@@ -10,7 +10,7 @@
 #include <QDir>
 #include <QSet>
 
-CacheForServiceRoot::CacheForServiceRoot() : m_cacheSaveMutex(new QMutex(QMutex::NonRecursive)) {}
+CacheForServiceRoot::CacheForServiceRoot() : m_cacheSaveMutex(new QMutex()) {}
 
 void CacheForServiceRoot::addLabelsAssignmentsToCache(const QList<Message>& ids_of_messages, Label* lbl, bool assign) {
   auto custom_ids = lbl->getParentServiceRoot()->customIDsOfMessages(ids_of_messages);
diff --git a/src/librssguard/services/gmail/gui/emailrecipientcontrol.cpp b/src/librssguard/services/gmail/gui/emailrecipientcontrol.cpp
index 67efafd68..2203a1ffc 100644
--- a/src/librssguard/services/gmail/gui/emailrecipientcontrol.cpp
+++ b/src/librssguard/services/gmail/gui/emailrecipientcontrol.cpp
@@ -18,7 +18,11 @@ EmailRecipientControl::EmailRecipientControl(const QString& recipient, QWidget*
   lay->addWidget(m_cmbRecipientType = new QComboBox(this));
   lay->addWidget(m_txtRecipient = new QLineEdit(this), 1);
   lay->addWidget(m_btnCloseMe = new PlainToolButton(this));
+
+#if QT_VERSION_MAJOR <= 5
   lay->setMargin(0);
+#endif
+
   lay->setContentsMargins(0, 0, 0, 0);
 
   m_cmbRecipientType->setFocusPolicy(Qt::FocusPolicy::NoFocus);
diff --git a/src/librssguard/services/gmail/gui/formaddeditemail.cpp b/src/librssguard/services/gmail/gui/formaddeditemail.cpp
index 0d71096d7..6475d342b 100644
--- a/src/librssguard/services/gmail/gui/formaddeditemail.cpp
+++ b/src/librssguard/services/gmail/gui/formaddeditemail.cpp
@@ -23,7 +23,10 @@ FormAddEditEmail::FormAddEditEmail(GmailServiceRoot* root, QWidget* parent)
 
   GuiUtilities::applyDialogProperties(*this, qApp->icons()->fromTheme(QSL("mail-message-new")));
 
+#if QT_VERSION_MAJOR <= 5
   m_ui.m_layoutAdder->setMargin(0);
+#endif
+
   m_ui.m_layoutAdder->setContentsMargins(0, 0, 0, 0);
 
   m_ui.m_btnAdder->setIcon(qApp->icons()->fromTheme(QSL("list-add")));