diff --git a/src/libsync/accessmanager.cpp b/src/libsync/accessmanager.cpp
index 4c19c20a196..fb131b02c21 100644
--- a/src/libsync/accessmanager.cpp
+++ b/src/libsync/accessmanager.cpp
@@ -93,6 +93,14 @@ QNetworkReply *AccessManager::createRequest(QNetworkAccessManager::Operation op,
     qInfo(lcAccessManager) << op << verb << newRequest.url().toString() << "has X-Request-ID" << requestId;
     newRequest.setRawHeader("X-Request-ID", requestId);
 
+#if QT_VERSION >= QT_VERSION_CHECK(5, 9, 0)
+    // only enable HTTP2 with Qt 5.9 because Qt 5.8.0 has too many bugs
+    // (only use one connection if the server does not support HTTP2)
+    if (newRequest.url().scheme() == "https") { // Not for "http": QTBUG-61397
+        newRequest.setAttribute(QNetworkRequest::HTTP2AllowedAttribute, true);
+    }
+#endif
+
     return QNetworkAccessManager::createRequest(op, newRequest, outgoingData);
 }
 
diff --git a/src/libsync/account.h b/src/libsync/account.h
index b34342d4525..de1cd0293c9 100644
--- a/src/libsync/account.h
+++ b/src/libsync/account.h
@@ -189,6 +189,10 @@ class OWNCLOUDSYNC_EXPORT Account : public QObject
     /** Detects a specific bug in older server versions */
     bool rootEtagChangesNotOnlySubFolderEtags();
 
+    /** True when the server supports HTTP2  */
+    bool isHttp2Supported() { return _http2Supported; }
+    void setHttp2Supported(bool value) { _http2Supported = value; };
+
     void clearCookieJar();
     void lendCookieJarTo(QNetworkAccessManager *guest);
     QString cookieJarPath();
@@ -247,6 +251,7 @@ protected Q_SLOTS:
     QuotaInfo *_quotaInfo;
     QSharedPointer<QNetworkAccessManager> _am;
     QScopedPointer<AbstractCredentials> _credentials;
+    bool _http2Supported = false;
 
     /// Certificates that were explicitly rejected by the user
     QList<QSslCertificate> _rejectedCertificates;
diff --git a/src/libsync/connectionvalidator.cpp b/src/libsync/connectionvalidator.cpp
index 0b5897f1ff6..9eff065dee5 100644
--- a/src/libsync/connectionvalidator.cpp
+++ b/src/libsync/connectionvalidator.cpp
@@ -282,10 +282,18 @@ bool ConnectionValidator::setAndCheckServerVersion(const QString &version)
         reportResult(ServerVersionMismatch);
         return false;
     }
-
     // We attempt to work with servers >= 5.0.0 but warn users.
     // Check usages of Account::serverVersionUnsupported() for details.
 
+#if QT_VERSION >= QT_VERSION_CHECK(5, 9, 0)
+    // Record that the server supports HTTP/2
+    if (auto job = qobject_cast<AbstractNetworkJob *>(sender())) {
+        if (auto reply = job->reply()) {
+            _account->setHttp2Supported(
+                reply->attribute(QNetworkRequest::HTTP2WasUsedAttribute).toBool());
+        }
+    }
+#endif
     return true;
 }
 
diff --git a/src/libsync/owncloudpropagator.cpp b/src/libsync/owncloudpropagator.cpp
index 016f0cdc84d..e76e00e8e15 100644
--- a/src/libsync/owncloudpropagator.cpp
+++ b/src/libsync/owncloudpropagator.cpp
@@ -84,18 +84,18 @@ int OwncloudPropagator::maximumActiveTransferJob()
         // disable parallelism when there is a network limit.
         return 1;
     }
-    return qCeil(hardMaximumActiveJob() / 2.);
+    return qMax(3, qCeil(hardMaximumActiveJob() / 2.));
 }
 
 /* The maximum number of active jobs in parallel  */
 int OwncloudPropagator::hardMaximumActiveJob()
 {
     static int max = qgetenv("OWNCLOUD_MAX_PARALLEL").toUInt();
-    if (!max) {
-        max = 6; //default (Qt cannot do more anyway)
-        // TODO: increase this number when using HTTP2
-    }
-    return max;
+    if (max)
+        return max;
+    if (_account->isHttp2Supported())
+        return 20;
+    return 6; // (Qt cannot do more anyway)
 }
 
 PropagateItemJob::~PropagateItemJob()
diff --git a/src/libsync/propagatedownload.cpp b/src/libsync/propagatedownload.cpp
index b5d6ac00406..2a6ca14394d 100644
--- a/src/libsync/propagatedownload.cpp
+++ b/src/libsync/propagatedownload.cpp
@@ -118,6 +118,8 @@ void GETFileJob::start()
         req.setRawHeader(it.key(), it.value());
     }
 
+    req.setPriority(QNetworkRequest::LowPriority); // Long downloads must not block non-propagation jobs.
+
     if (_directDownloadUrl.isEmpty()) {
         sendRequest("GET", makeDavUrl(path()), req);
     } else {
diff --git a/src/libsync/propagateupload.cpp b/src/libsync/propagateupload.cpp
index 757aee1c448..1cd0266277e 100644
--- a/src/libsync/propagateupload.cpp
+++ b/src/libsync/propagateupload.cpp
@@ -79,6 +79,8 @@ void PUTFileJob::start()
         req.setRawHeader(it.key(), it.value());
     }
 
+    req.setPriority(QNetworkRequest::LowPriority); // Long uploads must not block non-propagation jobs.
+
     if (_url.isValid()) {
         sendRequest("PUT", _url, req, _device);
     } else {
diff --git a/src/libsync/syncengine.cpp b/src/libsync/syncengine.cpp
index 8fa6eb7b726..967f5ca6a00 100644
--- a/src/libsync/syncengine.cpp
+++ b/src/libsync/syncengine.cpp
@@ -852,7 +852,7 @@ void SyncEngine::startSync()
     _discoveryMainThread->setParent(this);
     connect(this, SIGNAL(finished(bool)), _discoveryMainThread, SLOT(deleteLater()));
     qCInfo(lcEngine) << "Server" << account()->serverVersion()
-                     << QString("rootEtagChangesNotOnlySubFolderEtags=%1").arg(account()->rootEtagChangesNotOnlySubFolderEtags());
+                     << (account()->isHttp2Supported() ? "Using HTTP/2" : "");
     if (account()->rootEtagChangesNotOnlySubFolderEtags()) {
         connect(_discoveryMainThread, SIGNAL(etag(QString)), this, SLOT(slotRootEtagReceived(QString)));
     } else {