diff --git a/win32ss/include/ntuser.h b/win32ss/include/ntuser.h
index 846750ca64e..56e13e2229e 100644
--- a/win32ss/include/ntuser.h
+++ b/win32ss/include/ntuser.h
@@ -195,6 +195,15 @@ typedef struct tagIMC
     HWND           hImeWnd;
 } IMC, *PIMC;
 
+#ifndef _WIN64
+C_ASSERT(offsetof(IMC, head.h) == 0x0);
+C_ASSERT(offsetof(IMC, head.cLockObj) == 0x4);
+C_ASSERT(offsetof(IMC, head.pti) == 0x8);
+C_ASSERT(offsetof(IMC, pImcNext) == 0x14);
+C_ASSERT(offsetof(IMC, dwClientImcData) == 0x18);
+C_ASSERT(offsetof(IMC, hImeWnd) == 0x1c);
+#endif
+
 typedef struct _PROCDESKHEAD
 {
     HEAD;