diff --git a/mingw-w64-crt/lib32/user32.def b/mingw-w64-crt/lib32/user32.def
index f28deb5..4bdef9e 100755
--- a/mingw-w64-crt/lib32/user32.def
+++ b/mingw-w64-crt/lib32/user32.def
@@ -98,7 +98,7 @@
 CreateMDIWindowW@40
 CreateMenu@0
 CreatePopupMenu@0
-CreateSystemThreads@8
+CreateSystemThreads@16 ; ReactOS has the @8 variant
 CreateWindowExA@48
 CreateWindowExW@48
 CreateWindowStationA@16
@@ -426,8 +426,10 @@
 IsHungAppWindow@4
 IsIconic@4
 IsMenu@4
+IsProcess16Bit@0
 IsRectEmpty@4
 IsTouchWindow@8
+IsSETEnabled@0
 IsServerSideWindow@4
 IsWinEventHookInstalled@4
 IsWindow@4
@@ -435,6 +437,7 @@
 IsWindowInDestroy@4
 IsWindowUnicode@4
 IsWindowVisible@4
+IsWow64Message@0
 IsZoomed@4
 KillSystemTimer@8
 KillTimer@8
@@ -555,7 +558,7 @@
 RegisterShellHookWindow@4
 RegisterSystemThread@8
 RegisterTasklist@4
-RegisterUserApiHook@8
+RegisterUserApiHook@4 ; Prototype changed in 2003 - https://www.reactos.org/wiki/Techwiki:RegisterUserApiHook
 RegisterWindowMessageA@4
 RegisterWindowMessageW@4
 ReleaseCapture@0