diff --git a/src/gui/accountstate.cpp b/src/gui/accountstate.cpp
index 17cb3b16f30..eefd8c342bf 100644
--- a/src/gui/accountstate.cpp
+++ b/src/gui/accountstate.cpp
@@ -171,6 +171,22 @@ AccountState::AccountState(AccountPtr account)
         ownCloudGui::raise();
         msgBox->open();
     });
+
+
+    connect(_account->accessManager(), &AccessManager::isBehindCaptivePortalChanged, this, [this](bool onoff) {
+        if (onoff) {
+            _queueGuard.block();
+        } else {
+            // TODO: empty queue?
+            _queueGuard.unblock();
+        }
+    });
+    if (_account->accessManager()->isBehindCaptivePortal()) {
+        _queueGuard.block();
+    } else {
+        // TODO: empty queue?
+        _queueGuard.unblock();
+    }
 }
 
 AccountState::~AccountState() { }
@@ -247,6 +263,7 @@ void AccountState::setState(State state)
         } else if (_state == Connected && Utility::internetConnectionIsMetered() && ConfigFile().pauseSyncWhenMetered()) {
             _state = PausedDueToMetered;
         }
+        // Do we need an extra state PausedDueToCaptivePortal?
     }
 
     // might not have changed but the underlying _connectionErrors might have
diff --git a/src/gui/main.cpp b/src/gui/main.cpp
index d7fc389bf04..8ec844dd2ad 100644
--- a/src/gui/main.cpp
+++ b/src/gui/main.cpp
@@ -85,7 +85,7 @@ struct CommandLineOptions
     bool logFlush = false;
     bool logDebug = false;
 
-    bool debugMode = false;
+    bool debugMode = true;
 
     QString fileToOpen;
 };
diff --git a/src/gui/owncloudgui.cpp b/src/gui/owncloudgui.cpp
index 53520da5381..4d70023e4e1 100644
--- a/src/gui/owncloudgui.cpp
+++ b/src/gui/owncloudgui.cpp
@@ -641,17 +641,31 @@ void ownCloudGui::updateContextMenu()
     _contextMenu->addSeparator();
 
     if (_app->debugMode()) {
-        auto *crashMenu = _contextMenu->addMenu(QStringLiteral("Debug actions"));
-        crashMenu->addAction(QStringLiteral("Crash if asserts enabled - OC_ENSURE"), _app, [] {
+        auto *debugMenu = _contextMenu->addMenu(QStringLiteral("Debug actions"));
+        debugMenu->addAction(QStringLiteral("Crash if asserts enabled - OC_ENSURE"), _app, [] {
             if (OC_ENSURE(false)) {
                 Q_UNREACHABLE();
             }
         });
-        crashMenu->addAction(QStringLiteral("Crash if asserts enabled - Q_ASSERT"), _app, [] { Q_ASSERT(false); });
-        crashMenu->addAction(QStringLiteral("Crash now - Utility::crash()"), _app, [] { Utility::crash(); });
-        crashMenu->addAction(QStringLiteral("Crash now - OC_ENFORCE()"), _app, [] { OC_ENFORCE(false); });
-        crashMenu->addAction(QStringLiteral("Crash now - qFatal"), _app, [] { qFatal("la Qt fatale"); });
-        crashMenu->addAction(QStringLiteral("Restart now"), _app, [] { RestartManager::requestRestart(); });
+        debugMenu->addAction(QStringLiteral("Crash if asserts enabled - Q_ASSERT"), _app, [] { Q_ASSERT(false); });
+        debugMenu->addAction(QStringLiteral("Crash now - Utility::crash()"), _app, [] { Utility::crash(); });
+        debugMenu->addAction(QStringLiteral("Crash now - OC_ENFORCE()"), _app, [] { OC_ENFORCE(false); });
+        debugMenu->addAction(QStringLiteral("Crash now - qFatal"), _app, [] { qFatal("la Qt fatale"); });
+        debugMenu->addAction(QStringLiteral("Restart now"), _app, [] { RestartManager::requestRestart(); });
+        debugMenu->addSeparator();
+        auto captivePortalCheckbox = debugMenu->addAction(QStringLiteral("Behind Captive Portal"));
+        captivePortalCheckbox->setCheckable(true);
+
+        for (const auto &a : accountList) {
+            if (a->account()->accessManager()->forcedCaptivePortal()) {
+                captivePortalCheckbox->setChecked(true);
+            }
+        }
+        connect(captivePortalCheckbox, &QAction::triggered, [](bool checked) {
+            for (const auto &a : AccountManager::instance()->accounts()) {
+                a->account()->accessManager()->setForcedCaptivePortal(checked);
+            }
+        });
     }
 
     _contextMenu->addSeparator();
diff --git a/src/libsync/accessmanager.cpp b/src/libsync/accessmanager.cpp
index 35fe0659298..1f144be9930 100644
--- a/src/libsync/accessmanager.cpp
+++ b/src/libsync/accessmanager.cpp
@@ -16,6 +16,7 @@
 #include <QLoggingCategory>
 #include <QNetworkCookie>
 #include <QNetworkCookieJar>
+#include <QNetworkInformation>
 #include <QNetworkProxy>
 #include <QNetworkReply>
 #include <QNetworkRequest>
@@ -35,6 +36,7 @@ Q_LOGGING_CATEGORY(lcAccessManager, "sync.accessmanager", QtInfoMsg)
 
 AccessManager::AccessManager(QObject *parent)
     : QNetworkAccessManager(parent)
+    , _forcedCaptivePortal(false)
 {
     setCookieJar(new CookieJar);
 
@@ -47,6 +49,14 @@ AccessManager::AccessManager(QObject *parent)
             filtered.end());
         reply->ignoreSslErrors(filtered);
     });
+
+    if (auto *qNetInfo = QNetworkInformation::instance()) {
+        connect(qNetInfo, &QNetworkInformation::isBehindCaptivePortalChanged, this, [this](bool onoff) {
+            if (!_forcedCaptivePortal) {
+                emit isBehindCaptivePortalChanged(onoff);
+            }
+        });
+    }
 }
 
 QByteArray AccessManager::generateRequestId()
@@ -151,4 +161,39 @@ QList<QSslError> AccessManager::filterSslErrors(const QList<QSslError> &errors)
     return filtered;
 }
 
+bool AccessManager::isBehindCaptivePortal()
+{
+    if (_forcedCaptivePortal) {
+        return true;
+    }
+
+    if (auto *qNetInfo = QNetworkInformation::instance()) {
+        return qNetInfo->isBehindCaptivePortal();
+    }
+
+    return false;
+}
+
+bool AccessManager::forcedCaptivePortal()
+{
+    return _forcedCaptivePortal;
+}
+
+void AccessManager::setForcedCaptivePortal(bool onoff)
+{
+    if (_forcedCaptivePortal != onoff) {
+        _forcedCaptivePortal = onoff;
+        qCDebug(lcUtility) << "Switching forced captive portal to" << onoff;
+
+        if (auto *qNetInfo = QNetworkInformation::instance()) {
+            // Emit a signal only if we are/were simulating being behind a captive portal.
+            // In the case we were simulating (but stop doing so now), but in reality are still
+            // behind a portal, do not emit anything.
+            if (!qNetInfo->isBehindCaptivePortal()) {
+                emit isBehindCaptivePortalChanged(onoff);
+            }
+        }
+    }
+}
+
 } // namespace OCC
diff --git a/src/libsync/accessmanager.h b/src/libsync/accessmanager.h
index 75c1005132a..8375697dfb8 100644
--- a/src/libsync/accessmanager.h
+++ b/src/libsync/accessmanager.h
@@ -55,11 +55,19 @@ class OWNCLOUDSYNC_EXPORT AccessManager : public QNetworkAccessManager
      */
     QList<QSslError> filterSslErrors(const QList<QSslError> &errors) const;
 
+    bool isBehindCaptivePortal();
+    bool forcedCaptivePortal();
+    void setForcedCaptivePortal(bool onoff);
+
+signals:
+    void isBehindCaptivePortalChanged(bool state);
+
 protected:
     QNetworkReply *createRequest(QNetworkAccessManager::Operation op, const QNetworkRequest &request, QIODevice *outgoingData = nullptr) override;
 
 private:
     QSet<QSslCertificate> _customTrustedCaCertificates;
+    bool _forcedCaptivePortal;
 };
 
 } // namespace OCC
diff --git a/src/libsync/account.cpp b/src/libsync/account.cpp
index a53921ab4b2..f14fc1ac44c 100644
--- a/src/libsync/account.cpp
+++ b/src/libsync/account.cpp
@@ -172,11 +172,14 @@ AbstractCredentials *Account::credentials() const
 
 void Account::setCredentials(AbstractCredentials *cred)
 {
+    bool forcedCaptivePortal = false;
+
     // set active credential manager
     QNetworkCookieJar *jar = nullptr;
     if (_am) {
         jar = _am->cookieJar();
         jar->setParent(nullptr);
+        forcedCaptivePortal = _am->isBehindCaptivePortal();
         _am->deleteLater();
     }
 
@@ -186,6 +189,7 @@ void Account::setCredentials(AbstractCredentials *cred)
     cred->setAccount(this);
 
     _am = _credentials->createAM();
+    _am->setForcedCaptivePortal(forcedCaptivePortal);
 
     // the network access manager takes ownership when setCache is called, so we have to reinitialize it every time we reset the manager
     _networkCache = new QNetworkDiskCache(this);