diff --git a/dlls/msvcp140/msvcp140.spec b/dlls/msvcp140/msvcp140.spec
index 05d62becb12..fedb05fb88a 100644
--- a/dlls/msvcp140/msvcp140.spec
+++ b/dlls/msvcp140/msvcp140.spec
@@ -3675,10 +3675,10 @@
 @ stub _Mtx_clear_owner
 @ cdecl _Mtx_current_owns(ptr) msvcp110._Mtx_current_owns
 @ cdecl _Mtx_destroy(ptr) _Mtx_destroy
-@ stub _Mtx_destroy_in_situ
+@ cdecl _Mtx_destroy_in_situ(ptr) _Mtx_destroy_in_situ
 @ cdecl _Mtx_getconcrtcs(ptr) _Mtx_getconcrtcs
 @ cdecl _Mtx_init(ptr long) _Mtx_init
-@ stub _Mtx_init_in_situ
+@ cdecl _Mtx_init_in_situ(ptr long) _Mtx_init_in_situ
 @ cdecl _Mtx_lock(ptr) _Mtx_lock
 @ stub _Mtx_reset_owner
 @ stub _Mtx_timedlock
diff --git a/dlls/msvcp90/misc.c b/dlls/msvcp90/misc.c
index 18b6a198ad6..322e937719c 100644
--- a/dlls/msvcp90/misc.c
+++ b/dlls/msvcp90/misc.c
@@ -478,19 +478,29 @@ typedef _Mtx_t *_Mtx_arg_t;
 #define MTX_T_TO_ARG(m)     (&(m))
 #endif
 
-int __cdecl _Mtx_init(_Mtx_t *mtx, int flags)
+void __cdecl _Mtx_init_in_situ(_Mtx_t mtx, int flags)
 {
     if(flags & ~MTX_MULTI_LOCK)
         FIXME("unknown flags ignored: %x\n", flags);
 
+    mtx->flags = flags;
+    call_func1(critical_section_ctor, &mtx->cs);
+    mtx->thread_id = -1;
+    mtx->count = 0;
+}
+
+int __cdecl _Mtx_init(_Mtx_t *mtx, int flags)
+{
     *mtx = MSVCRT_operator_new(sizeof(**mtx));
-    (*mtx)->flags = flags;
-    call_func1(critical_section_ctor, &(*mtx)->cs);
-    (*mtx)->thread_id = -1;
-    (*mtx)->count = 0;
+    _Mtx_init_in_situ(*mtx, flags);
     return 0;
 }
 
+void __cdecl _Mtx_destroy_in_situ(_Mtx_t mtx)
+{
+    call_func1(critical_section_dtor, &mtx->cs);
+}
+
 void __cdecl _Mtx_destroy(_Mtx_arg_t mtx)
 {
     call_func1(critical_section_dtor, &MTX_T_FROM_ARG(mtx)->cs);