diff --git a/src/plugins/coreplugin/idocumentfactory.cpp b/src/plugins/coreplugin/idocumentfactory.cpp
index 0d8280dc080..8730c6b01f1 100644
--- a/src/plugins/coreplugin/idocumentfactory.cpp
+++ b/src/plugins/coreplugin/idocumentfactory.cpp
@@ -46,10 +46,10 @@ const QList<IDocumentFactory *> IDocumentFactory::allDocumentFactories()
     return g_documentFactories;
 }
 
-IDocument *IDocumentFactory::open(const QString &filename)
+IDocument *IDocumentFactory::open(const Utils::FilePath &filePath)
 {
     QTC_ASSERT(m_opener, return nullptr);
-    return m_opener(filename);
+    return m_opener(filePath);
 }
 
 } // namespace Core
diff --git a/src/plugins/coreplugin/idocumentfactory.h b/src/plugins/coreplugin/idocumentfactory.h
index 796eca0eb6c..bd60cc52ae6 100644
--- a/src/plugins/coreplugin/idocumentfactory.h
+++ b/src/plugins/coreplugin/idocumentfactory.h
@@ -33,6 +33,8 @@
 
 #include <functional>
 
+namespace Utils { class FilePath; }
+
 namespace Core {
 
 class IDocument;
@@ -45,8 +47,8 @@ public:
 
     static const QList<IDocumentFactory *> allDocumentFactories();
 
-    using Opener = std::function<IDocument *(const QString &fileName)>;
-    IDocument *open(const QString &filename);
+    using Opener = std::function<IDocument *(const Utils::FilePath &filePath)>;
+    IDocument *open(const Utils::FilePath &filePath);
 
     QStringList mimeTypes() const { return m_mimeTypes; }
 
diff --git a/src/plugins/coreplugin/mainwindow.cpp b/src/plugins/coreplugin/mainwindow.cpp
index 4029f1a5575..95de5c7f02d 100644
--- a/src/plugins/coreplugin/mainwindow.cpp
+++ b/src/plugins/coreplugin/mainwindow.cpp
@@ -892,7 +892,7 @@ IDocument *MainWindow::openFiles(const FilePaths &filePaths,
         const QFileInfo fi(workingDir, fileName);
         const QString absoluteFilePath = fi.absoluteFilePath();
         if (IDocumentFactory *documentFactory = findDocumentFactory(documentFactories, filePath)) {
-            IDocument *document = documentFactory->open(absoluteFilePath);
+            IDocument *document = documentFactory->open(FilePath::fromString(absoluteFilePath));
             if (!document) {
                 if (flags & ICore::StopOnLoadFail)
                     return res;
diff --git a/src/plugins/projectexplorer/projectexplorer.cpp b/src/plugins/projectexplorer/projectexplorer.cpp
index b55b75c0e47..f6893e6c50c 100644
--- a/src/plugins/projectexplorer/projectexplorer.cpp
+++ b/src/plugins/projectexplorer/projectexplorer.cpp
@@ -2081,12 +2081,15 @@ void ProjectExplorerPlugin::extensionsInitialized()
     const QString filterSeparator = QLatin1String(";;");
     QStringList filterStrings;
 
-    dd->m_documentFactory.setOpener([](QString fileName) {
-        const QFileInfo fi(fileName);
-        if (fi.isDir())
-            fileName = FolderNavigationWidget::projectFilesInDirectory(fi.absoluteFilePath()).value(0, fileName);
+    dd->m_documentFactory.setOpener([](FilePath filePath) {
+        if (filePath.isDir()) {
+            const QStringList files =
+                FolderNavigationWidget::projectFilesInDirectory(filePath.absoluteFilePath().toString());
+            if (!files.isEmpty())
+                filePath = FilePath::fromString(files.front());
+        }
 
-        OpenProjectResult result = ProjectExplorerPlugin::openProject(FilePath::fromString(fileName));
+        OpenProjectResult result = ProjectExplorerPlugin::openProject(filePath);
         if (!result)
             showOpenProjectError(result);
         return nullptr;
diff --git a/src/plugins/tasklist/tasklistplugin.cpp b/src/plugins/tasklist/tasklistplugin.cpp
index d41996dcdec..6684f86a92c 100644
--- a/src/plugins/tasklist/tasklistplugin.cpp
+++ b/src/plugins/tasklist/tasklistplugin.cpp
@@ -209,8 +209,8 @@ bool TaskListPlugin::initialize(const QStringList &arguments, QString *errorMess
     TaskHub::addCategory(Constants::TASKLISTTASK_ID, tr("My Tasks"));
 
     d->m_fileFactory.addMimeType(QLatin1String("text/x-tasklist"));
-    d->m_fileFactory.setOpener([this](const QString &fileName) {
-        return openTasks(FilePath::fromString(fileName));
+    d->m_fileFactory.setOpener([this](const FilePath &filePath) {
+        return openTasks(filePath);
     });
 
     connect(SessionManager::instance(), &SessionManager::sessionLoaded,