diff --git a/src/libs/utils/CMakeLists.txt b/src/libs/utils/CMakeLists.txt
index 9db6ea5f1e7..b94b2b42227 100644
--- a/src/libs/utils/CMakeLists.txt
+++ b/src/libs/utils/CMakeLists.txt
@@ -168,6 +168,7 @@ add_qtc_library(Utils
     textfileformat.cpp textfileformat.h
     textutils.cpp textutils.h
     theme/theme.cpp theme/theme.h theme/theme_p.h
+    threadutils.cpp threadutils.h
     tooltip/effects.h
     tooltip/tips.cpp tooltip/tips.h
     tooltip/tooltip.cpp tooltip/tooltip.h
diff --git a/src/libs/utils/threadutils.cpp b/src/libs/utils/threadutils.cpp
new file mode 100644
index 00000000000..7d10199c4ab
--- /dev/null
+++ b/src/libs/utils/threadutils.cpp
@@ -0,0 +1,38 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#include "threadutils.h"
+
+#include <QCoreApplication>
+#include <QThread>
+
+namespace Utils {
+
+bool isMainThread()
+{
+    return QThread::currentThread() == qApp->thread();
+}
+
+} // namespace Utils
diff --git a/src/libs/utils/threadutils.h b/src/libs/utils/threadutils.h
new file mode 100644
index 00000000000..cc59658c277
--- /dev/null
+++ b/src/libs/utils/threadutils.h
@@ -0,0 +1,35 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+#include "utils_global.h"
+
+namespace Utils {
+
+QTCREATOR_UTILS_EXPORT bool isMainThread();
+
+} // namespace Utils
+
diff --git a/src/libs/utils/utils-lib.pri b/src/libs/utils/utils-lib.pri
index ddaae4bb697..a8280ba3267 100644
--- a/src/libs/utils/utils-lib.pri
+++ b/src/libs/utils/utils-lib.pri
@@ -143,6 +143,7 @@ SOURCES += \
     $$PWD/link.cpp \
     $$PWD/linecolumn.cpp \
     $$PWD/multitextcursor.cpp \
+    $$PWD/threadutils.cpp \
     $$PWD/singleton.cpp
 
 HEADERS += \
@@ -310,6 +311,7 @@ HEADERS += \
     $$PWD/launchersocket.h \
     $$PWD/qtcsettings.h \
     $$PWD/multitextcursor.h \
+    $$PWD/threadutils.h \
     $$PWD/singleton.h
 
 FORMS += $$PWD/filewizardpage.ui \
diff --git a/src/libs/utils/utils.qbs b/src/libs/utils/utils.qbs
index 77f80dd81b8..6d888f87ac4 100644
--- a/src/libs/utils/utils.qbs
+++ b/src/libs/utils/utils.qbs
@@ -298,6 +298,8 @@ Project {
             "textfileformat.h",
             "textutils.cpp",
             "textutils.h",
+            "threadutils.cpp",
+            "threadutils.h",
             "treemodel.cpp",
             "treemodel.h",
             "treeviewcombobox.cpp",
diff --git a/src/plugins/cmakeprojectmanager/fileapidataextractor.cpp b/src/plugins/cmakeprojectmanager/fileapidataextractor.cpp
index 7200a060002..d5836605f48 100644
--- a/src/plugins/cmakeprojectmanager/fileapidataextractor.cpp
+++ b/src/plugins/cmakeprojectmanager/fileapidataextractor.cpp
@@ -757,7 +757,7 @@ FileApiQtcData extractData(FileApiData &input,
     result.projectParts = generateRawProjectParts(data, sourceDirectory, buildDirectory);
 
     auto rootProjectNode = generateRootProjectNode(data, sourceDirectory, buildDirectory);
-    ProjectTree::applyTreeManager(rootProjectNode.get()); // QRC nodes
+    ProjectTree::applyTreeManager(rootProjectNode.get(), ProjectTree::AsyncPhase); // QRC nodes
     result.rootProjectNode = std::move(rootProjectNode);
 
     setupLocationInfoForTargets(result.rootProjectNode.get(), result.buildTargets);
diff --git a/src/plugins/coreplugin/documentmanager.cpp b/src/plugins/coreplugin/documentmanager.cpp
index d7d5f17d8f1..4fd4213dbbb 100644
--- a/src/plugins/coreplugin/documentmanager.cpp
+++ b/src/plugins/coreplugin/documentmanager.cpp
@@ -55,6 +55,7 @@
 #include <utils/pathchooser.h>
 #include <utils/qtcassert.h>
 #include <utils/reloadpromptutils.h>
+#include <utils/threadutils.h>
 
 #include <QStringList>
 #include <QDateTime>
@@ -326,6 +327,7 @@ static void addFileInfo(IDocument *document, const FilePath &filePath, const Fil
    (The added file names are guaranteed to be absolute and cleaned.) */
 static void addFileInfos(const QList<IDocument *> &documents)
 {
+    QTC_ASSERT(isMainThread(), return);
     FilePaths pathsToWatch;
     FilePaths linkPathsToWatch;
     for (IDocument *document : documents) {
@@ -400,6 +402,7 @@ void DocumentManager::addDocuments(const QList<IDocument *> &documents, bool add
 */
 static void removeFileInfo(IDocument *document)
 {
+    QTC_ASSERT(isMainThread(), return);
     if (!d->m_documentsWithWatch.contains(document))
         return;
     foreach (const FilePath &filePath, d->m_documentsWithWatch.value(document)) {
diff --git a/src/plugins/projectexplorer/project.cpp b/src/plugins/projectexplorer/project.cpp
index 620eb61f5fa..38cdf161713 100644
--- a/src/plugins/projectexplorer/project.cpp
+++ b/src/plugins/projectexplorer/project.cpp
@@ -586,7 +586,8 @@ void Project::setRootProjectNode(std::unique_ptr<ProjectNode> &&root)
     }
 
     if (root) {
-        ProjectTree::applyTreeManager(root.get());
+        ProjectTree::applyTreeManager(root.get(), ProjectTree::AsyncPhase);
+        ProjectTree::applyTreeManager(root.get(), ProjectTree::FinalPhase);
         root->setParentFolderNode(d->m_containerNode.get());
     }
 
diff --git a/src/plugins/projectexplorer/projecttree.cpp b/src/plugins/projectexplorer/projecttree.cpp
index aa8e79f9efb..ee040d5a37f 100644
--- a/src/plugins/projectexplorer/projecttree.cpp
+++ b/src/plugins/projectexplorer/projecttree.cpp
@@ -402,13 +402,13 @@ void ProjectTree::registerTreeManager(const TreeManagerFunction &treeChange)
         s_instance->m_treeManagers.append(treeChange);
 }
 
-void ProjectTree::applyTreeManager(FolderNode *folder)
+void ProjectTree::applyTreeManager(FolderNode *folder, ConstructionPhase phase)
 {
     if (!folder)
         return;
 
     for (TreeManagerFunction &f : s_instance->m_treeManagers)
-        f(folder);
+        f(folder, phase);
 }
 
 bool ProjectTree::hasNode(const Node *node)
diff --git a/src/plugins/projectexplorer/projecttree.h b/src/plugins/projectexplorer/projecttree.h
index 060dad22903..3947666d3a6 100644
--- a/src/plugins/projectexplorer/projecttree.h
+++ b/src/plugins/projectexplorer/projecttree.h
@@ -68,6 +68,11 @@ public:
         const bool m_active = false;
     };
 
+    enum ConstructionPhase {
+        AsyncPhase,
+        FinalPhase
+    };
+
     // Integration with ProjectTreeWidget
     static void registerWidget(Internal::ProjectTreeWidget *widget);
     static void unregisterWidget(Internal::ProjectTreeWidget *widget);
@@ -79,9 +84,9 @@ public:
 
     static void highlightProject(Project *project, const QString &message);
 
-    using TreeManagerFunction = std::function<void(FolderNode *)>;
+    using TreeManagerFunction = std::function<void(FolderNode *, ConstructionPhase)>;
     static void registerTreeManager(const TreeManagerFunction &treeChange);
-    static void applyTreeManager(FolderNode *folder);
+    static void applyTreeManager(FolderNode *folder, ConstructionPhase phase);
 
     // Nodes:
     static bool hasNode(const Node *node);
diff --git a/src/plugins/projectexplorer/treescanner.cpp b/src/plugins/projectexplorer/treescanner.cpp
index ce6da40b1c2..88e7b8d4a83 100644
--- a/src/plugins/projectexplorer/treescanner.cpp
+++ b/src/plugins/projectexplorer/treescanner.cpp
@@ -159,7 +159,7 @@ static std::unique_ptr<FolderNode> createFolderNode(const Utils::FilePath &direc
         std::unique_ptr<FileNode> node(fn->clone());
         fileSystemNode->addNestedNode(std::move(node));
     }
-    ProjectTree::applyTreeManager(fileSystemNode.get()); // QRC nodes
+    ProjectTree::applyTreeManager(fileSystemNode.get(), ProjectTree::AsyncPhase); // QRC nodes
     return fileSystemNode;
 }
 
diff --git a/src/plugins/qbsprojectmanager/qbsnodetreebuilder.cpp b/src/plugins/qbsprojectmanager/qbsnodetreebuilder.cpp
index c481975753f..7e3c31c378a 100644
--- a/src/plugins/qbsprojectmanager/qbsnodetreebuilder.cpp
+++ b/src/plugins/qbsprojectmanager/qbsnodetreebuilder.cpp
@@ -232,7 +232,7 @@ QbsProjectNode *QbsNodeTreeBuilder::buildTree(const QString &projectName,
     }
     buildSystemFiles->compress();
     root->addNode(std::move(buildSystemFiles));
-    ProjectTree::applyTreeManager(root.get()); // QRC nodes
+    ProjectTree::applyTreeManager(root.get(), ProjectTree::AsyncPhase); // QRC nodes
     return root.release();
 }
 
diff --git a/src/plugins/resourceeditor/resourceeditorplugin.cpp b/src/plugins/resourceeditor/resourceeditorplugin.cpp
index 62a4d752456..f901a417dff 100644
--- a/src/plugins/resourceeditor/resourceeditorplugin.cpp
+++ b/src/plugins/resourceeditor/resourceeditorplugin.cpp
@@ -46,6 +46,7 @@
 #include <utils/algorithm.h>
 #include <utils/parameteraction.h>
 #include <utils/qtcassert.h>
+#include <utils/threadutils.h>
 
 #include <QCoreApplication>
 #include <QAction>
@@ -247,21 +248,33 @@ ResourceEditorPluginPrivate::ResourceEditorPluginPrivate(ResourceEditorPlugin *q
 
 void ResourceEditorPlugin::extensionsInitialized()
 {
-    ProjectTree::registerTreeManager([](FolderNode *folder) {
-        QList<FileNode *> toReplace;
-        folder->forEachNode([&toReplace](FileNode *fn) {
-            if (fn->fileType() == FileType::Resource)
-                toReplace.append(fn);
-        });
-
-        for (FileNode *file : qAsConst(toReplace)) {
-            FolderNode *const pn = file->parentFolderNode();
-            QTC_ASSERT(pn, continue);
-            const Utils::FilePath path = file->filePath();
-            auto topLevel = std::make_unique<ResourceTopLevelNode>(path, pn->filePath());
-            topLevel->setEnabled(file->isEnabled());
-            topLevel->setIsGenerated(file->isGenerated());
-            pn->replaceSubtree(file, std::move(topLevel));
+    ProjectTree::registerTreeManager([](FolderNode *folder, ProjectTree::ConstructionPhase phase) {
+        switch (phase) {
+        case ProjectTree::AsyncPhase: {
+            QList<FileNode *> toReplace;
+            folder->forEachNode([&toReplace](FileNode *fn) {
+                if (fn->fileType() == FileType::Resource)
+                    toReplace.append(fn);
+            });
+            for (FileNode *file : qAsConst(toReplace)) {
+                FolderNode *const pn = file->parentFolderNode();
+                QTC_ASSERT(pn, continue);
+                const Utils::FilePath path = file->filePath();
+                auto topLevel = std::make_unique<ResourceTopLevelNode>(path, pn->filePath());
+                topLevel->setEnabled(file->isEnabled());
+                topLevel->setIsGenerated(file->isGenerated());
+                pn->replaceSubtree(file, std::move(topLevel));
+            }
+            break;
+        }
+        case ProjectTree::FinalPhase: {
+            folder->forEachNode({}, [](FolderNode *fn) {
+                auto *topLevel = dynamic_cast<ResourceTopLevelNode *>(fn);
+                if (topLevel)
+                    topLevel->setupWatcherIfNeeded();
+            });
+            break;
+        }
         }
     });
 }
diff --git a/src/plugins/resourceeditor/resourcenode.cpp b/src/plugins/resourceeditor/resourcenode.cpp
index 30be6b0c0a3..75f35da4d8a 100644
--- a/src/plugins/resourceeditor/resourcenode.cpp
+++ b/src/plugins/resourceeditor/resourcenode.cpp
@@ -36,6 +36,7 @@
 #include <utils/fileutils.h>
 #include <utils/mimetypes/mimedatabase.h>
 #include <utils/qtcassert.h>
+#include <utils/threadutils.h>
 
 #include <QCoreApplication>
 #include <QDir>
@@ -251,10 +252,8 @@ ResourceTopLevelNode::ResourceTopLevelNode(const FilePath &filePath,
     setShowWhenEmpty(true);
 
     if (!filePath.isEmpty()) {
-        if (filePath.isReadableFile()) {
-            m_document = new ResourceFileWatcher(this);
-            DocumentManager::addDocument(m_document);
-        }
+        if (filePath.isReadableFile())
+            setupWatcherIfNeeded();
     } else {
         m_contents = contents;
     }
@@ -267,6 +266,15 @@ ResourceTopLevelNode::ResourceTopLevelNode(const FilePath &filePath,
     addInternalNodes();
 }
 
+void ResourceTopLevelNode::setupWatcherIfNeeded()
+{
+    if (m_document || !isMainThread())
+        return;
+
+    m_document = new ResourceFileWatcher(this);
+    DocumentManager::addDocument(m_document);
+}
+
 ResourceTopLevelNode::~ResourceTopLevelNode()
 {
     if (m_document)
diff --git a/src/plugins/resourceeditor/resourcenode.h b/src/plugins/resourceeditor/resourcenode.h
index a992e267dc8..03ae8039f0c 100644
--- a/src/plugins/resourceeditor/resourcenode.h
+++ b/src/plugins/resourceeditor/resourcenode.h
@@ -39,6 +39,7 @@ public:
                          const QString &contents = {});
     ~ResourceTopLevelNode() override;
 
+    void setupWatcherIfNeeded();
     void addInternalNodes();
 
     bool supportsAction(ProjectExplorer::ProjectAction action, const Node *node) const override;