diff --git a/src/plugins/qmldesigner/components/itemlibrary/customfilesystemmodel.cpp b/src/plugins/qmldesigner/components/itemlibrary/customfilesystemmodel.cpp
index 549c4ea4483..db16051072a 100644
--- a/src/plugins/qmldesigner/components/itemlibrary/customfilesystemmodel.cpp
+++ b/src/plugins/qmldesigner/components/itemlibrary/customfilesystemmodel.cpp
@@ -120,7 +120,7 @@ public:
     QIcon icon( const QFileInfo & info ) const override
     {
         QIcon icon;
-        const QString suffix = info.suffix();
+        const QString suffix = info.suffix().toLower();
         const QString filePath = info.absoluteFilePath();
 
         // Provide icon depending on suffix
@@ -288,7 +288,7 @@ void CustomFileSystemModel::setSearchFilter(const QString &nameFilterList)
 QPair<QString, QByteArray> CustomFileSystemModel::resourceTypeAndData(const QModelIndex &index) const
 {
     QFileInfo fi = fileInfo(index);
-    QString suffix = fi.suffix();
+    QString suffix = fi.suffix().toLower();
     if (!suffix.isEmpty()) {
         if (supportedImageSuffixes().contains(suffix)) {
             // Data: Image format (suffix)
@@ -365,16 +365,17 @@ QModelIndex CustomFileSystemModel::updatePath(const QString &newPath)
         nameFilterList.append(QString(QStringLiteral("*%1*")).arg(searchFilter));
     } else {
         const QString filterTemplate("*%1*.%2");
-        for (const QString &ext : supportedImageSuffixes())
-            nameFilterList.append(filterTemplate.arg(searchFilter, ext));
-        for (const QString &ext : supportedShaderSuffixes())
-            nameFilterList.append(filterTemplate.arg(searchFilter, ext));
-        for (const QString &ext : supportedFontSuffixes())
-            nameFilterList.append(filterTemplate.arg(searchFilter, ext));
-        for (const QString &ext : supportedAudioSuffixes())
-            nameFilterList.append(filterTemplate.arg(searchFilter, ext));
-        for (const QString &ext : supportedTexture3DSuffixes())
-            nameFilterList.append(filterTemplate.arg(searchFilter, ext));
+        auto appendFilters = [&](const QStringList &suffixes) {
+            for (const QString &ext : suffixes) {
+                nameFilterList.append(filterTemplate.arg(searchFilter, ext));
+                nameFilterList.append(filterTemplate.arg(searchFilter, ext.toUpper()));
+            }
+        };
+        appendFilters(supportedImageSuffixes());
+        appendFilters(supportedShaderSuffixes());
+        appendFilters(supportedFontSuffixes());
+        appendFilters(supportedAudioSuffixes());
+        appendFilters(supportedTexture3DSuffixes());
     }
 
     m_files.clear();
diff --git a/src/plugins/qmldesigner/components/itemlibrary/itemlibraryassetimportdialog.cpp b/src/plugins/qmldesigner/components/itemlibrary/itemlibraryassetimportdialog.cpp
index e49ffbb9bf0..f16e2a1c0af 100644
--- a/src/plugins/qmldesigner/components/itemlibrary/itemlibraryassetimportdialog.cpp
+++ b/src/plugins/qmldesigner/components/itemlibrary/itemlibraryassetimportdialog.cpp
@@ -88,7 +88,7 @@ ItemLibraryAssetImportDialog::ItemLibraryAssetImportDialog(const QStringList &im
     // Skip unsupported assets
     QHash<QString, bool> supportMap;
     for (const auto &file : importFiles) {
-        QString suffix = QFileInfo(file).suffix();
+        QString suffix = QFileInfo(file).suffix().toLower();
         if (!supportMap.contains(suffix)) {
             bool supported = false;
             for (const auto &exts : supportedExts) {
diff --git a/src/plugins/qmldesigner/components/itemlibrary/itemlibrarywidget.cpp b/src/plugins/qmldesigner/components/itemlibrary/itemlibrarywidget.cpp
index ccc9c595c17..34d9201360d 100644
--- a/src/plugins/qmldesigner/components/itemlibrary/itemlibrarywidget.cpp
+++ b/src/plugins/qmldesigner/components/itemlibrary/itemlibrarywidget.cpp
@@ -210,7 +210,7 @@ ItemLibraryWidget::ItemLibraryWidget(AsynchronousImageCache &imageCache,
         const QList<QUrl> urls = event->mimeData()->urls();
         for (const QUrl &url : urls) {
             QFileInfo fi(url.toLocalFile());
-            if (suffixes.contains(fi.suffix())) {
+            if (suffixes.contains(fi.suffix().toLower())) {
                 accept = true;
                 break;
             }
@@ -564,7 +564,7 @@ void ItemLibraryWidget::importDroppedFiles(const QList<Utils::DropSupport::FileS
     QStringList fileNames;
     for (const auto &file : files) {
         QFileInfo fi(file.filePath);
-        if (m_resourcesFileSystemModel->supportedSuffixes().contains(fi.suffix()))
+        if (m_resourcesFileSystemModel->supportedSuffixes().contains(fi.suffix().toLower()))
             fileNames.append(fi.absoluteFilePath());
     }
     if (!fileNames.isEmpty())