diff --git a/win32ss/include/ntuser.h b/win32ss/include/ntuser.h
index 0ffa9ea15d9..dee47c9e9e7 100644
--- a/win32ss/include/ntuser.h
+++ b/win32ss/include/ntuser.h
@@ -1235,13 +1235,17 @@ typedef struct tagIMEUI
     DWORD dwLastStatus;
 } IMEUI, *PIMEUI;
 
-/* Window Extra data container. */
-typedef struct _IMEWND
+typedef struct tagIMEWND
 {
     WND wnd;
     PIMEUI pimeui;
 } IMEWND, *PIMEWND;
 
+#define GWLP_IMEWND_PIMEUI 0
+
+/* IMEWND and GWLP_IMEWND_PIMEUI assume this alignment */
+C_ASSERT(sizeof(WND) % sizeof(PVOID) == 0);
+
 DWORD
 NTAPI
 NtUserAssociateInputContext(
diff --git a/win32ss/user/ntuser/ime.c b/win32ss/user/ntuser/ime.c
index ec84f155e27..d897c67369c 100644
--- a/win32ss/user/ntuser/ime.c
+++ b/win32ss/user/ntuser/ime.c
@@ -40,6 +40,13 @@ typedef struct tagIMEHOTKEY
 PIMEHOTKEY gpImeHotKeyList = NULL;
 LCID glcidSystem = 0;
 
+static inline PIMEUI FASTCALL IntGetImeUIFromWnd(_In_ PWND pWnd)
+{
+    ASSERT(pWnd->cbwndExtra >= sizeof(PIMEUI));
+    PIMEWND pImeWnd = (PIMEWND)pWnd;
+    return pImeWnd->pimeui;
+}
+
 static DWORD FASTCALL
 IntGetImeCompatFlags(_In_opt_ PTHREADINFO pti)
 {
@@ -2089,10 +2096,11 @@ co_IntCreateDefaultImeWindow(
     pImeWnd = co_UserCreateWindowEx(&Cs, &ClassName, (PLARGE_STRING)&WindowName, NULL, WINVER);
     if (pImeWnd)
     {
-        pimeui = ((PIMEWND)pImeWnd)->pimeui;
+        pimeui = IntGetImeUIFromWnd(pImeWnd);
+        ASSERT(pimeui);
         _SEH2_TRY
         {
-            ProbeForWrite(pimeui, sizeof(IMEUI), 1);
+            ProbeForWrite(pimeui, sizeof(*pimeui), 1);
             pimeui->fDefault = TRUE;
             if (IS_WND_CHILD(pwndTarget) && pwndTarget->spwndParent->head.pti != pti)
                 pimeui->fChildThreadDef = TRUE;
@@ -2118,8 +2126,8 @@ IntImeCanDestroyDefIMEforChild(
     PIMEUI pimeui;
     IMEUI SafeImeUI;
 
-    pimeui = ((PIMEWND)pImeWnd)->pimeui;
-    if (!pimeui || (LONG_PTR)pimeui == (LONG_PTR)-1)
+    pimeui = IntGetImeUIFromWnd(pImeWnd);
+    if (!pimeui)
         return FALSE;
 
     // Check IMEUI.fChildThreadDef
@@ -2165,8 +2173,8 @@ IntImeCanDestroyDefIME(
     PIMEUI pimeui;
     IMEUI SafeImeUI;
 
-    pimeui = ((PIMEWND)pImeWnd)->pimeui;
-    if (!pimeui || (LONG_PTR)pimeui == (LONG_PTR)-1)
+    pimeui = IntGetImeUIFromWnd(pImeWnd);
+    if (!pimeui)
         return FALSE;
 
     // Check IMEUI.fDestroy
@@ -2257,8 +2265,8 @@ IntCheckImeShowStatus(
             continue;
         }
 
-        pimeui = ((PIMEWND)pwndNode)->pimeui;
-        if (!pimeui || pimeui == (PIMEUI)-1)
+        pimeui = IntGetImeUIFromWnd(pwndNode);
+        if (!pimeui)
             continue;
 
         if (pti && pti != pwndNode->head.pti)
@@ -2425,7 +2433,7 @@ IntSendOpenStatusNotify(PTHREADINFO ptiIME, PIMEUI pimeui, PWND pWnd, BOOL bOpen
     }
 }
 
-// Update the IME status and send a notification.
+// Update the IME toolbar visibility and send a notification
 VOID FASTCALL
 IntNotifyImeShowStatus(_In_ PWND pImeWnd)
 {
@@ -2441,6 +2449,13 @@ IntNotifyImeShowStatus(_In_ PWND pImeWnd)
     pti = PsGetCurrentThreadWin32Thread();
     ptiIME = pImeWnd->head.pti;
 
+    pimeui = IntGetImeUIFromWnd(pImeWnd);
+    if (!pimeui)
+    {
+        ERR("Invalid IMEWND %p\n", pImeWnd);
+        return;
+    }
+
     // Attach to the process if necessary
     if (pti != ptiIME)
         KeAttachProcess(&(ptiIME->ppi->peProcess->Pcb));
@@ -2448,8 +2463,7 @@ IntNotifyImeShowStatus(_In_ PWND pImeWnd)
     // Get an IMEUI and check whether hwndIMC is valid and update fShowStatus
     _SEH2_TRY
     {
-        ProbeForWrite(pImeWnd, sizeof(IMEWND), 1);
-        pimeui = ((PIMEWND)pImeWnd)->pimeui;
+        ProbeForWrite(pimeui, sizeof(*pimeui), 1);
         SafeImeUI = *pimeui;
 
         bShow = (gfIMEShowStatus == TRUE) && SafeImeUI.fCtrlShowStatus;
@@ -2466,7 +2480,7 @@ IntNotifyImeShowStatus(_In_ PWND pImeWnd)
     }
     _SEH2_EXCEPT(EXCEPTION_EXECUTE_HANDLER)
     {
-        ERR("Exception in IntNotifyImeShowStatus: %p, %p, %p, %d, %d\n", 
+        ERR("Exception in IntNotifyImeShowStatus: %p, %p, %p, %d, %d\n",
             pImeWnd, pimeui, ptiIME, SafeImeUI.fCtrlShowStatus, gfIMEShowStatus);
 
         if (pti != ptiIME)
diff --git a/win32ss/user/user32/controls/regcontrol.c b/win32ss/user/user32/controls/regcontrol.c
index 3360841ffc6..6d80f6c25dc 100644
--- a/win32ss/user/user32/controls/regcontrol.c
+++ b/win32ss/user/user32/controls/regcontrol.c
@@ -65,6 +65,7 @@ static const struct
 /*    { &ICONTITLE_builtin_class, FNID_ICONTITLE, ICLS_ICONTITLE}, // moved to win32k */
     { &STATIC_builtin_class,    FNID_STATIC,    ICLS_STATIC},
     { &GHOST_builtin_class,     FNID_GHOST,     ICLS_GHOST},
+    { &IME_builtin_class,       FNID_IME,       ICLS_IME},
 };
 
 BOOL WINAPI RegisterSystemControls(VOID)
@@ -81,6 +82,12 @@ BOOL WINAPI RegisterSystemControls(VOID)
 
     for (i = 0; i != sizeof(g_SysClasses) / sizeof(g_SysClasses[0]); i++)
     {
+        if (g_SysClasses[i].fnid == FNID_IME)
+        {
+            if (!IS_IMM_MODE() || (RegisterDefaultClasses & ICLASS_TO_MASK(ICLS_IME)))
+                continue;
+        }
+
         WndClass.lpszClassName = g_SysClasses[i].desc->name;
 
         // Set Global bit!
@@ -99,12 +106,6 @@ BOOL WINAPI RegisterSystemControls(VOID)
            RegisterDefaultClasses |= ICLASS_TO_MASK(g_SysClasses[i].ClsId);
     }
 
-    if ( //gpsi->dwSRVIFlags & SRVINFO_IMM32 && Not supported yet, need NlsMbCodePageTag working in Win32k.
-        !(RegisterDefaultClasses & ICLASS_TO_MASK(ICLS_IME))) // So, work like XP.
-    {
-       RegisterIMEClass();
-    }
-
     return TRUE;
 }
 
diff --git a/win32ss/user/user32/include/regcontrol.h b/win32ss/user/user32/include/regcontrol.h
index f1b3b69bf03..c84ee0d9694 100644
--- a/win32ss/user/user32/include/regcontrol.h
+++ b/win32ss/user/user32/include/regcontrol.h
@@ -39,6 +39,7 @@ extern const struct builtin_class_descr MENU_builtin_class;
 extern const struct builtin_class_descr SCROLL_builtin_class;
 extern const struct builtin_class_descr STATIC_builtin_class;
 extern const struct builtin_class_descr GHOST_builtin_class;
+extern const struct builtin_class_descr IME_builtin_class;
 
 ATOM WINAPI RegisterClassExWOWW(WNDCLASSEXW *,LPDWORD,WORD,DWORD,BOOL);
 BOOL FASTCALL VersionRegisterClass(PCWSTR,LPCWSTR,HANDLE,HMODULE *);
@@ -46,4 +47,3 @@ BOOL FASTCALL VersionRegisterClass(PCWSTR,LPCWSTR,HANDLE,HMODULE *);
 LRESULT WINAPI ImeWndProc_common(HWND,UINT,WPARAM,LPARAM,BOOL);
 LRESULT WINAPI ImeWndProcA(HWND,UINT,WPARAM,LPARAM);
 LRESULT WINAPI ImeWndProcW(HWND,UINT,WPARAM,LPARAM);
-BOOL WINAPI RegisterIMEClass(VOID);
diff --git a/win32ss/user/user32/misc/imm.c b/win32ss/user/user32/misc/imm.c
index 44c88d52c4e..4a455b864f9 100644
--- a/win32ss/user/user32/misc/imm.c
+++ b/win32ss/user/user32/misc/imm.c
@@ -1009,20 +1009,27 @@ ImeWndProc_common(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam, BOOL unicod
         return 0;
     }
 
-    pimeui = (PIMEUI)GetWindowLongPtrW(hwnd, 0);
-    if (pimeui == NULL)
+    if (msg == WM_NCCREATE)
     {
         pimeui = HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, sizeof(IMEUI));
-        if (pimeui == NULL)
+        if (!pimeui)
         {
             ERR("HeapAlloc failed\n");
             NtUserSetWindowFNID(hwnd, FNID_DESTROY);
-            DestroyWindow(hwnd);
+            return FALSE;
+        }
+        pimeui->spwnd = pWnd;
+        SetWindowLongPtrW(hwnd, GWLP_IMEWND_PIMEUI, (LONG_PTR)pimeui);
+    }
+    else
+    {
+        pimeui = (PIMEUI)GetWindowLongPtrW(hwnd, GWLP_IMEWND_PIMEUI);
+        if (!pimeui)
+        {
+            ERR("Invalid IMEWND\n");
+            NtUserSetWindowFNID(hwnd, FNID_DESTROY);
             return 0;
         }
-
-        SetWindowLongPtrW(hwnd, 0, (LONG_PTR)pimeui);
-        pimeui->spwnd = pWnd;
     }
 
     if (IS_CICERO_MODE())
@@ -1173,30 +1180,16 @@ BOOL WINAPI UpdatePerUserImmEnabling(VOID)
     return ret;
 }
 
-BOOL
-WINAPI
-RegisterIMEClass(VOID)
+const struct builtin_class_descr IME_builtin_class =
 {
-    ATOM atom;
-    WNDCLASSEXW WndClass = { sizeof(WndClass) };
-
-    WndClass.lpszClassName  = L"IME";
-    WndClass.style          = CS_GLOBALCLASS;
-    WndClass.lpfnWndProc    = ImeWndProcW;
-    WndClass.cbWndExtra     = sizeof(LONG_PTR);
-    WndClass.hCursor        = LoadCursorW(NULL, IDC_ARROW);
-
-    atom = RegisterClassExWOWW(&WndClass, 0, FNID_IME, 0, FALSE);
-    if (!atom)
-    {
-        ERR("Failed to register IME Class!\n");
-        return FALSE;
-    }
-
-    RegisterDefaultClasses |= ICLASS_TO_MASK(ICLS_IME);
-    TRACE("RegisterIMEClass atom = %u\n", atom);
-    return TRUE;
-}
+    L"IME",                       /* name */
+    CS_GLOBALCLASS,               /* style */
+    ImeWndProcA,                  /* procA */
+    ImeWndProcW,                  /* procW */
+    sizeof(IMEWND) - sizeof(WND), /* extra */
+    IDC_ARROW,                    /* cursor */
+    NULL                          /* brush */
+};
 
 /*
  * @implemented