diff --git a/src/FolderWindow.cpp b/src/FolderWindow.cpp
index 4c7758b..1dd3cbe 100644
--- a/src/FolderWindow.cpp
+++ b/src/FolderWindow.cpp
@@ -17,8 +17,6 @@
 
 namespace chromafiler {
 
-const wchar_t FOLDER_WINDOW_CLASS[] = L"ChromaFile Folder";
-
 const wchar_t PROP_SHELL_VISITED[] = L"Visited";
 const wchar_t PROP_ICON_POS[] = L"IconPos";
 
@@ -59,8 +57,6 @@ bool FolderWindow::spatialView(IFolderView *const folderView) {
 }
 
 void FolderWindow::init() {
-    RegisterClass(tempPtr(createWindowClass(FOLDER_WINDOW_CLASS)));
-
     for (int i = 0; i < _countof(HIDDEN_ITEM_PARSE_NAMES); i++) {
         CComPtr<IShellItem> item;
         if (SUCCEEDED(SHCreateItemFromParsingName(HIDDEN_ITEM_PARSE_NAMES[i], nullptr,
@@ -76,10 +72,6 @@ void FolderWindow::init() {
 FolderWindow::FolderWindow(ItemWindow *const parent, IShellItem *const item)
         : ItemWindow(parent, item) {}
 
-const wchar_t * FolderWindow::className() const {
-    return FOLDER_WINDOW_CLASS;
-}
-
 bool FolderWindow::persistSizeInParent() const {
     return false;
 }
diff --git a/src/FolderWindow.h b/src/FolderWindow.h
index 77504ae..78d5e96 100644
--- a/src/FolderWindow.h
+++ b/src/FolderWindow.h
@@ -161,8 +161,6 @@ class FolderWindow : public ItemWindow, public IServiceProvider, public ICommDlg
         std::unique_ptr<POINT[]> itemPositions;
     };
 
-    const wchar_t * className() const override;
-
     void listViewCreated();
     static LRESULT CALLBACK listViewSubclassProc(HWND hwnd, UINT message,
         WPARAM wParam, LPARAM lParam, UINT_PTR subclassID, DWORD_PTR refData);
diff --git a/src/ItemWindow.cpp b/src/ItemWindow.cpp
index c18bc30..1634891 100644
--- a/src/ItemWindow.cpp
+++ b/src/ItemWindow.cpp
@@ -20,6 +20,7 @@
 
 namespace chromafiler {
 
+const wchar_t ITEM_WINDOW_CLASS[] = L"ChromaFiler Item Window";
 const wchar_t TESTPOS_CLASS[] = L"ChromaFiler Test Window";
 const wchar_t WINDOW_THEME[] = L"CompositedWindow::Window";
 const UINT SC_DRAGMOVE = SC_MOVE | 2; // https://stackoverflow.com/a/35880547/11525734
@@ -97,6 +98,17 @@ void ItemWindow::init() {
 
     HINSTANCE hInstance = GetModuleHandle(nullptr);
 
+    WNDCLASS itemClass = {};
+    itemClass.lpfnWndProc = windowProc;
+    itemClass.hInstance = hInstance;
+    itemClass.lpszClassName = ITEM_WINDOW_CLASS;
+    if (!compositionEnabled)
+        itemClass.style = CS_HREDRAW; // redraw caption when resizing
+    // change toolbar color
+    if (IsWindows10OrGreater())
+        itemClass.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
+    RegisterClass(&itemClass);
+
     WNDCLASS testPosClass = {};
     testPosClass.lpszClassName = TESTPOS_CLASS;
     testPosClass.lpfnWndProc = DefWindowProc;
@@ -163,19 +175,6 @@ void ItemWindow::uninit() {
         RemoveFontMemResourceEx(symbolFontHandle);
 }
 
-WNDCLASS ItemWindow::createWindowClass(const wchar_t *name) {
-    WNDCLASS wndClass = {};
-    wndClass.lpfnWndProc = windowProc;
-    wndClass.hInstance = GetModuleHandle(nullptr);
-    wndClass.lpszClassName = name;
-    if (!compositionEnabled)
-        wndClass.style = CS_HREDRAW; // redraw caption when resizing
-    // change toolbar color
-    if (IsWindows10OrGreater())
-        wndClass.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
-    return wndClass;
-}
-
 void ItemWindow::flashWindow(HWND hwnd) {
     PostMessage(hwnd, MSG_FLASH_WINDOW, 0, 0);
 }
@@ -185,6 +184,10 @@ ItemWindow::ItemWindow(ItemWindow *const parent, IShellItem *const item)
           item(item),
           proxyIcon(this) {}
 
+const wchar_t * ItemWindow::className() const {
+    return ITEM_WINDOW_CLASS;
+}
+
 void ItemWindow::setScratch(bool value) {
     scratch = value;
 }
diff --git a/src/ItemWindow.h b/src/ItemWindow.h
index 007937b..d6ff4e0 100644
--- a/src/ItemWindow.h
+++ b/src/ItemWindow.h
@@ -65,7 +65,6 @@ class ItemWindow : public WindowImpl, public IUnknownImpl {
         MSG_FLASH_WINDOW,
         MSG_LAST
     };
-    static WNDCLASS createWindowClass(const wchar_t *name);
     LRESULT handleMessage(UINT message, WPARAM wParam, LPARAM lParam) override;
 
     virtual SIZE defaultSize() const;
@@ -155,7 +154,7 @@ class ItemWindow : public WindowImpl, public IUnknownImpl {
     CComQIPtr<IContextMenu3> contextMenu3;
 
 private:
-    virtual const wchar_t * className() const = 0;
+    virtual const wchar_t * className() const;
 
     bool centeredProxy() const; // requires useCustomFrame() == true
 
diff --git a/src/PreviewWindow.cpp b/src/PreviewWindow.cpp
index 4713bdb..8efbd2f 100644
--- a/src/PreviewWindow.cpp
+++ b/src/PreviewWindow.cpp
@@ -8,7 +8,6 @@ namespace chromafiler {
 
 // https://geelaw.blog/entries/ipreviewhandlerframe-wpf-2-interop/
 
-const wchar_t PREVIEW_WINDOW_CLASS[] = L"ChromaFile Preview";
 const wchar_t PREVIEW_CONTAINER_CLASS[] = L"ChromaFile Preview Container";
 
 const int FACTORY_CACHE_SIZE = 4;
@@ -31,8 +30,6 @@ static FactoryCacheEntry factoryCache[FACTORY_CACHE_SIZE] = {};
 static int factoryCacheIndex = 0;
 
 void PreviewWindow::init() {
-    RegisterClass(tempPtr(createWindowClass(PREVIEW_WINDOW_CLASS)));
-
     WNDCLASS containerClass = {};
     containerClass.lpszClassName = PREVIEW_CONTAINER_CLASS;
     containerClass.lpfnWndProc = DefWindowProc;
@@ -57,10 +54,6 @@ PreviewWindow::PreviewWindow(ItemWindow *const parent, IShellItem *const item, C
     : ItemWindow(parent, item),
       previewID(previewID) {}
 
-const wchar_t * PreviewWindow::className() const {
-    return PREVIEW_WINDOW_CLASS;
-}
-
 void PreviewWindow::onCreate() {
     ItemWindow::onCreate();
 
diff --git a/src/PreviewWindow.h b/src/PreviewWindow.h
index 769645d..617148c 100644
--- a/src/PreviewWindow.h
+++ b/src/PreviewWindow.h
@@ -51,8 +51,6 @@ class PreviewWindow : public ItemWindow, public IPreviewHandlerFrame {
     void refresh() override;
 
 private:
-    const wchar_t * className() const override;
-
     void destroyPreview();
 
     CLSID previewID;
diff --git a/src/TextWindow.cpp b/src/TextWindow.cpp
index 145ef20..68c17e0 100644
--- a/src/TextWindow.cpp
+++ b/src/TextWindow.cpp
@@ -12,8 +12,6 @@
 
 namespace chromafiler {
 
-const wchar_t TEXT_WINDOW_CLASS[] = L"ChromaFile Text";
-
 const wchar_t PROP_WORD_WRAP[] = L"WordWrap";
 
 const ULONG MAX_FILE_SIZE = 50'000'000;
@@ -36,8 +34,6 @@ static UINT updateSettingsMessage, findReplaceMessage;
 static HMODULE hMsftedit = nullptr;
 
 void TextWindow::init() {
-    RegisterClass(tempPtr(createWindowClass(TEXT_WINDOW_CLASS)));
-
     textAccelTable = LoadAccelerators(GetModuleHandle(nullptr), MAKEINTRESOURCE(IDR_TEXT_ACCEL));
 
     updateSettingsMessage = checkLE(RegisterWindowMessage(L"chromafiler_TextUpdateSettings"));
@@ -61,10 +57,6 @@ TextWindow::TextWindow(ItemWindow *const parent, IShellItem *const item)
     replaceBuffer[0] = 0;
 }
 
-const wchar_t * TextWindow::className() const {
-    return TEXT_WINDOW_CLASS;
-}
-
 const wchar_t * TextWindow::appUserModelID() const {
     return L"chroma.text";
 }
diff --git a/src/TextWindow.h b/src/TextWindow.h
index a5d5116..88c974a 100644
--- a/src/TextWindow.h
+++ b/src/TextWindow.h
@@ -58,8 +58,6 @@ class TextWindow : public ItemWindow {
     void trackContextMenu(POINT pos) override;
 
 private:
-    const wchar_t * className() const override;
-
     HWND createRichEdit(bool readOnly, bool wordWrap);
     bool isEditable();
     CComPtr<ITextDocument> getTOMDocument();
diff --git a/src/ThumbnailWindow.cpp b/src/ThumbnailWindow.cpp
index fa1c4bc..a14ce08 100644
--- a/src/ThumbnailWindow.cpp
+++ b/src/ThumbnailWindow.cpp
@@ -6,14 +6,6 @@
 
 namespace chromafiler {
 
-const wchar_t THUMBNAIL_WINDOW_CLASS[] = L"ChromaFile Thumbnail";
-
-void ThumbnailWindow::init() {
-    WNDCLASS wndClass = createWindowClass(THUMBNAIL_WINDOW_CLASS);
-    wndClass.style |= CS_HREDRAW | CS_VREDRAW; // redraw whenever size changes
-    RegisterClass(&wndClass);
-}
-
 ThumbnailWindow::ThumbnailWindow(ItemWindow *const parent, IShellItem *const item)
     : ItemWindow(parent, item) {}
 
@@ -25,10 +17,6 @@ ThumbnailWindow::~ThumbnailWindow() {
     }
 }
 
-const wchar_t * ThumbnailWindow::className() const {
-    return THUMBNAIL_WINDOW_CLASS;
-}
-
 void ThumbnailWindow::onCreate() {
     ItemWindow::onCreate();
     thumbnailThread.Attach(new ThumbnailThread(item, this));
@@ -45,6 +33,7 @@ void ThumbnailWindow::onSize(SIZE size) {
     RECT bodyRect = windowBody();
     SIZE bodySize = rectSize(bodyRect);
     thumbnailThread->requestThumbnail(bodySize);
+    // TODO invalidate?
 }
 
 void ThumbnailWindow::onItemChanged() {
diff --git a/src/ThumbnailWindow.h b/src/ThumbnailWindow.h
index f18c3a4..a6d0f46 100644
--- a/src/ThumbnailWindow.h
+++ b/src/ThumbnailWindow.h
@@ -7,8 +7,6 @@ namespace chromafiler {
 
 class ThumbnailWindow : public ItemWindow {
 public:
-    static void init();
-
     ThumbnailWindow(ItemWindow *parent, IShellItem *item);
     ~ThumbnailWindow();
 
@@ -29,8 +27,6 @@ class ThumbnailWindow : public ItemWindow {
     void refresh() override;
 
 private:
-    const wchar_t * className() const override;
-
     SRWLOCK thumbnailBitmapLock = SRWLOCK_INIT;
     HBITMAP thumbnailBitmap = nullptr;
 
diff --git a/src/TrayWindow.cpp b/src/TrayWindow.cpp
index 2642108..8f9d809 100644
--- a/src/TrayWindow.cpp
+++ b/src/TrayWindow.cpp
@@ -9,7 +9,7 @@
 
 namespace chromafiler {
 
-const wchar_t TRAY_WINDOW_CLASS[] = L"ChromaFile Tray";
+const wchar_t TRAY_WINDOW_CLASS[] = L"ChromaFile Tray"; // used by installer, do not change!
 
 const int HOTKEY_FOCUS_TRAY = 1;
 
@@ -43,8 +43,10 @@ static void snapAxis(LONG value, LONG edge, LONG *snapOffset, LONG *snapDist) {
 }
 
 void TrayWindow::init() {
-    WNDCLASS wndClass = createWindowClass(TRAY_WINDOW_CLASS);
-    wndClass.style = 0; // clear redraw style
+    WNDCLASS wndClass = {};
+    wndClass.lpfnWndProc = windowProc;
+    wndClass.hInstance = GetModuleHandle(nullptr);
+    wndClass.lpszClassName = TRAY_WINDOW_CLASS;
     wndClass.hbrBackground = (HBRUSH)(COLOR_3DFACE + 1);
     RegisterClass(&wndClass);
 
diff --git a/src/main.cpp b/src/main.cpp
index 3e18cd2..858ef7c 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1,6 +1,5 @@
 #include "main.h"
 #include "FolderWindow.h"
-#include "ThumbnailWindow.h"
 #include "PreviewWindow.h"
 #include "TextWindow.h"
 #include "TrayWindow.h"
@@ -110,7 +109,6 @@ int WINAPI wWinMain(HINSTANCE, HINSTANCE, PWSTR, int showCommand) {
     initDPI();
     ItemWindow::init();
     FolderWindow::init();
-    ThumbnailWindow::init();
     PreviewWindow::init();
     TextWindow::init();
     TrayWindow::init();