diff --git a/dll/win32/imm32/imm.c b/dll/win32/imm32/imm.c
index d1fa849150e..7b0b415f74f 100644
--- a/dll/win32/imm32/imm.c
+++ b/dll/win32/imm32/imm.c
@@ -784,7 +784,7 @@ static void ImmInternalSendIMEMessage(InputContextData *data, UINT msg, WPARAM w
 
 static InputContextData* get_imc_data(HIMC hIMC)
 {
-    InputContextData *data = hIMC;
+    InputContextData *data = (InputContextData *)hIMC;
 
     if (hIMC == NULL)
         return NULL;
@@ -861,7 +861,7 @@ HIMC WINAPI ImmAssociateContext(HWND hWnd, HIMC hIMC)
 
         if (old)
         {
-            InputContextData *old_data = old;
+            InputContextData *old_data = (InputContextData *)old;
             if (old_data->IMC.hWnd == hWnd)
                 old_data->IMC.hWnd = NULL;
         }
@@ -2546,7 +2546,7 @@ HIMC WINAPI ImmGetContext(HWND hWnd)
 
     if (rc)
     {
-        InputContextData *data = rc;
+        InputContextData *data = (InputContextData *)rc;
         data->IMC.hWnd = hWnd;
     }
 
@@ -3340,26 +3340,38 @@ BOOL WINAPI ImmIsIME(HKL hKL)
     return !!ImmGetImeInfoEx(&info, ImeInfoExImeWindow, &hKL);
 }
 
+static BOOL APIENTRY
+ImmIsUIMessageAW(HWND hWndIME, UINT msg, WPARAM wParam, LPARAM lParam, BOOL bAnsi)
+{
+    switch (msg)
+    {
+        case WM_IME_STARTCOMPOSITION: case WM_IME_ENDCOMPOSITION:
+        case WM_IME_COMPOSITION: case WM_IME_SETCONTEXT: case WM_IME_NOTIFY:
+        case WM_IME_COMPOSITIONFULL: case WM_IME_SELECT: case WM_IME_SYSTEM:
+            break;
+        default:
+            return FALSE;
+    }
+
+    if (!hWndIME)
+        return TRUE;
+
+    if (bAnsi)
+        SendMessageA(hWndIME, msg, wParam, lParam);
+    else
+        SendMessageW(hWndIME, msg, wParam, lParam);
+
+    return TRUE;
+}
+
 /***********************************************************************
  *		ImmIsUIMessageA (IMM32.@)
  */
 BOOL WINAPI ImmIsUIMessageA(
   HWND hWndIME, UINT msg, WPARAM wParam, LPARAM lParam)
 {
-    TRACE("(%p, %x, %ld, %ld)\n", hWndIME, msg, wParam, lParam);
-    if ((msg >= WM_IME_STARTCOMPOSITION && msg <= WM_IME_KEYLAST) ||
-            (msg == WM_IME_SETCONTEXT) ||
-            (msg == WM_IME_NOTIFY) ||
-            (msg == WM_IME_COMPOSITIONFULL) ||
-            (msg == WM_IME_SELECT) ||
-            (msg == 0x287 /* FIXME: WM_IME_SYSTEM */))
-    {
-        if (hWndIME)
-            SendMessageA(hWndIME, msg, wParam, lParam);
-
-        return TRUE;
-    }
-    return FALSE;
+    TRACE("(%p, 0x%X, %p, %p)\n", hWndIME, msg, wParam, lParam);
+    return ImmIsUIMessageAW(hWndIME, msg, wParam, lParam, TRUE);
 }
 
 /***********************************************************************
@@ -3368,20 +3380,8 @@ BOOL WINAPI ImmIsUIMessageA(
 BOOL WINAPI ImmIsUIMessageW(
   HWND hWndIME, UINT msg, WPARAM wParam, LPARAM lParam)
 {
-    TRACE("(%p, %x, %ld, %ld)\n", hWndIME, msg, wParam, lParam);
-    if ((msg >= WM_IME_STARTCOMPOSITION && msg <= WM_IME_KEYLAST) ||
-            (msg == WM_IME_SETCONTEXT) ||
-            (msg == WM_IME_NOTIFY) ||
-            (msg == WM_IME_COMPOSITIONFULL) ||
-            (msg == WM_IME_SELECT) ||
-            (msg == 0x287 /* FIXME: WM_IME_SYSTEM */))
-    {
-        if (hWndIME)
-            SendMessageW(hWndIME, msg, wParam, lParam);
-
-        return TRUE;
-    }
-    return FALSE;
+    TRACE("(%p, 0x%X, %p, %p)\n", hWndIME, msg, wParam, lParam);
+    return ImmIsUIMessageAW(hWndIME, msg, wParam, lParam, FALSE);
 }
 
 /***********************************************************************
@@ -4543,7 +4543,7 @@ BOOL WINAPI ImmTranslateMessage(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lKeyD
     TRACE("%p %x %x %x\n",hwnd, msg, (UINT)wParam, (UINT)lKeyData);
 
     if (imc)
-        data = imc;
+        data = (InputContextData *)imc;
     else
         return FALSE;
 
@@ -4602,7 +4602,7 @@ BOOL WINAPI ImmProcessKey(HWND hwnd, HKL hKL, UINT vKey, LPARAM lKeyData, DWORD
     TRACE("%p %p %x %x %x\n",hwnd, hKL, vKey, (UINT)lKeyData, unknown);
 
     if (imc)
-        data = imc;
+        data = (InputContextData *)imc;
     else
         return FALSE;
 
@@ -4800,7 +4800,7 @@ BOOL WINAPI User32InitializeImmEntryTable(DWORD);
 BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpReserved)
 {
     HKL hKL;
-    HWND hWnd;
+    HIMC hIMC;
     PTEB pTeb;
 
     TRACE("(%p, 0x%X, %p)\n", hinstDLL, fdwReason, lpReserved);
@@ -4833,8 +4833,9 @@ BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpReserved)
                 return TRUE;
 
             hKL = GetKeyboardLayout(0);
-            hWnd = (HWND)Imm32GetThreadState(THREADSTATE_CAPTUREWINDOW);
-            Imm32CleanupContext(hWnd, hKL, TRUE);
+            // FIXME: NtUserGetThreadState and enum ThreadStateRoutines are broken.
+            hIMC = (HIMC)Imm32GetThreadState(4);
+            Imm32CleanupContext(hIMC, hKL, TRUE);
             break;
 
         case DLL_PROCESS_DETACH:
diff --git a/dll/win32/imm32/imm32.spec b/dll/win32/imm32/imm32.spec
index e196f08627a..bca6da02f8a 100644
--- a/dll/win32/imm32/imm32.spec
+++ b/dll/win32/imm32/imm32.spec
@@ -66,8 +66,8 @@
 @ stdcall ImmInstallIMEA(str str)
 @ stdcall ImmInstallIMEW(wstr wstr)
 @ stdcall ImmIsIME(long)
-@ stdcall ImmIsUIMessageA(long long long long)
-@ stdcall ImmIsUIMessageW(long long long long)
+@ stdcall ImmIsUIMessageA(ptr long ptr ptr)
+@ stdcall ImmIsUIMessageW(ptr long ptr ptr)
 @ stdcall ImmLoadIME(ptr)
 @ stdcall ImmLoadLayout(ptr ptr)
 @ stdcall ImmLockClientImc(ptr)
diff --git a/modules/rostests/apitests/imm32/clientimc.c b/modules/rostests/apitests/imm32/clientimc.c
index 99ed8423537..0f43024efd0 100644
--- a/modules/rostests/apitests/imm32/clientimc.c
+++ b/modules/rostests/apitests/imm32/clientimc.c
@@ -28,11 +28,11 @@ START_TEST(clientimc)
     pClientImc->cLockObj = 2;
     pClientImc->dwFlags = 0x40;
     RtlInitializeCriticalSection(&pClientImc->cs);
-    ok_long(ImmGetIMCCSize(pClientImc->hImc), 4);
+    ok_long(ImmGetIMCCSize((HIMCC)pClientImc->hImc), 4);
 
     ImmUnlockClientImc(pClientImc);
     ok_long(pClientImc->cLockObj, 1);
-    ok_long(ImmGetIMCCSize(pClientImc->hImc), 4);
+    ok_long(ImmGetIMCCSize((HIMCC)pClientImc->hImc), 4);
 
     dwCode = 0;
     _SEH2_TRY
@@ -47,7 +47,7 @@ START_TEST(clientimc)
     ok_long(dwCode, STATUS_ACCESS_VIOLATION);
 
     ok_long(pClientImc->cLockObj, 0);
-    ok_long(ImmGetIMCCSize(pClientImc->hImc), 0);
+    ok_long(ImmGetIMCCSize((HIMCC)pClientImc->hImc), 0);
 
     HeapFree(GetProcessHeap(), 0, pClientImc);
 }
diff --git a/modules/rostests/winetests/imm32/imm32.c b/modules/rostests/winetests/imm32/imm32.c
index 040a43fc058..fef5b0dbb0d 100644
--- a/modules/rostests/winetests/imm32/imm32.c
+++ b/modules/rostests/winetests/imm32/imm32.c
@@ -606,9 +606,17 @@ static void test_ImmIME(void)
     if (imc)
     {
         BOOL rc;
+#ifdef __REACTOS__
+        rc = ImmConfigureIMEA((HKL)imc, NULL, IME_CONFIG_REGISTERWORD, NULL);
+#else
         rc = ImmConfigureIMEA(imc, NULL, IME_CONFIG_REGISTERWORD, NULL);
+#endif
         ok (rc == 0, "ImmConfigureIMEA did not fail\n");
+#ifdef __REACTOS__
+        rc = ImmConfigureIMEW((HKL)imc, NULL, IME_CONFIG_REGISTERWORD, NULL);
+#else
         rc = ImmConfigureIMEW(imc, NULL, IME_CONFIG_REGISTERWORD, NULL);
+#endif
         ok (rc == 0, "ImmConfigureIMEW did not fail\n");
     }
     ImmReleaseContext(hwnd,imc);
diff --git a/sdk/include/psdk/imm.h b/sdk/include/psdk/imm.h
index 7b0888b033e..7fc769ee1eb 100644
--- a/sdk/include/psdk/imm.h
+++ b/sdk/include/psdk/imm.h
@@ -25,10 +25,13 @@
 extern "C" {
 #endif
 
+#ifdef __REACTOS__
+DECLARE_HANDLE(HIMC);
+DECLARE_HANDLE(HIMCC);
+typedef HKL *LPHKL;
+#else
 typedef HANDLE HIMC;
 typedef HANDLE HIMCC;
-#ifdef __REACTOS__
-typedef HKL *LPHKL;
 #endif
 
 typedef struct tagREGISTERWORDA {
diff --git a/win32ss/include/ntuser.h b/win32ss/include/ntuser.h
index 26e89fb396a..3147acfac6f 100644
--- a/win32ss/include/ntuser.h
+++ b/win32ss/include/ntuser.h
@@ -6,9 +6,8 @@ struct _THREADINFO;
 struct _DESKTOP;
 struct _WND;
 struct tagPOPUPMENU;
-#ifndef HIMC
-typedef HANDLE HIMC;
-#endif
+
+#define WM_IME_SYSTEM 0x287
 
 #define FIRST_USER_HANDLE 0x0020 /* first possible value for low word of user handle */
 #define LAST_USER_HANDLE 0xffef /* last possible value for low word of user handle */