diff --git a/src/plugins/help/helpplugin.cpp b/src/plugins/help/helpplugin.cpp
index 4ae12c70c7f..b5c82ab8dc7 100644
--- a/src/plugins/help/helpplugin.cpp
+++ b/src/plugins/help/helpplugin.cpp
@@ -444,8 +444,13 @@ void HelpPlugin::updateSideBarSource()
 
 void HelpPlugin::updateSideBarSource(const QUrl &newUrl)
 {
-    if (m_rightPaneSideBarWidget)
-        m_rightPaneSideBarWidget->currentViewer()->setSource(newUrl);
+    if (m_rightPaneSideBarWidget) {
+        // This is called when setSource on the central widget is called.
+        // Avoid nested setSource calls (even of different help viewers) by scheduling the
+        // sidebar viewer update on the event loop (QTCREATORBUG-12742)
+        QMetaObject::invokeMethod(m_rightPaneSideBarWidget->currentViewer(), "setSource",
+                                  Qt::QueuedConnection, Q_ARG(QUrl, newUrl));
+    }
 }
 
 void HelpPlugin::fontChanged()
diff --git a/src/plugins/help/helpviewer.h b/src/plugins/help/helpviewer.h
index e57f3e20b5c..8672f53f88c 100644
--- a/src/plugins/help/helpviewer.h
+++ b/src/plugins/help/helpviewer.h
@@ -59,7 +59,8 @@ public:
     virtual QString title() const = 0;
 
     virtual QUrl source() const = 0;
-    virtual void setSource(const QUrl &url) = 0;
+    // metacall in HelpPlugin::updateSideBarSource
+    Q_INVOKABLE virtual void setSource(const QUrl &url) = 0;
     virtual void scrollToAnchor(const QString &anchor) = 0;
     virtual void highlightId(const QString &id) { Q_UNUSED(id) }