diff --git a/reactos/dll/ntdll/def/ntdll.pspec b/reactos/dll/ntdll/def/ntdll.pspec
index d1ae0cbd155..7eb3e5519e9 100644
--- a/reactos/dll/ntdll/def/ntdll.pspec
+++ b/reactos/dll/ntdll/def/ntdll.pspec
@@ -895,7 +895,7 @@
 @ stdcall RtlSetSecurityObject(long ptr ptr ptr ptr)
 //@ stdcall RtlSetSecurityObjectEx
 //@ stdcall RtlSetThreadErrorMode
-//@ stdcall RtlSetThreadIsCritical
+@ stdcall RtlSetThreadIsCritical(long ptr long)
 //@ stdcall RtlSetThreadPoolStartFunc
 @ stdcall RtlSetTimeZoneInformation(ptr)
 //@ stdcall RtlSetTimer
diff --git a/reactos/dll/ntdll/def/ntdll.spec b/reactos/dll/ntdll/def/ntdll.spec
index d1026472f2d..ec779e88411 100644
--- a/reactos/dll/ntdll/def/ntdll.spec
+++ b/reactos/dll/ntdll/def/ntdll.spec
@@ -895,7 +895,7 @@
 @ stdcall RtlSetSecurityObject(long ptr ptr ptr ptr)
 ;@ stdcall RtlSetSecurityObjectEx
 ;@ stdcall RtlSetThreadErrorMode
-;@ stdcall RtlSetThreadIsCritical
+@ stdcall RtlSetThreadIsCritical(long ptr long)
 ;@ stdcall RtlSetThreadPoolStartFunc
 @ stdcall RtlSetTimeZoneInformation(ptr)
 ;@ stdcall RtlSetTimer
diff --git a/reactos/include/ndk/rtlfuncs.h b/reactos/include/ndk/rtlfuncs.h
index 50b2a0bd3b3..081027cc763 100644
--- a/reactos/include/ndk/rtlfuncs.h
+++ b/reactos/include/ndk/rtlfuncs.h
@@ -2406,6 +2406,15 @@ RtlSetProcessIsCritical(
     IN BOOLEAN NeedBreaks
 );
 
+NTSYSAPI
+NTSTATUS
+NTAPI
+RtlSetThreadIsCritical(
+    IN BOOLEAN NewValue,
+    OUT PBOOLEAN OldValue OPTIONAL,
+    IN BOOLEAN NeedBreaks
+);
+
 NTSYSAPI
 ULONG
 NTAPI
diff --git a/reactos/include/reactos/subsys/sm/smmsg.h b/reactos/include/reactos/subsys/sm/smmsg.h
index 5c30ff24cc3..cf60d8871bc 100644
--- a/reactos/include/reactos/subsys/sm/smmsg.h
+++ b/reactos/include/reactos/subsys/sm/smmsg.h
@@ -53,6 +53,7 @@ typedef struct _SM_EXEC_PGM_MSG
     RTL_USER_PROCESS_INFORMATION ProcessInformation;
     BOOLEAN DebugFlag;
 } SM_EXEC_PGM_MSG, *PM_EXEC_PGM_MSG;
+C_ASSERT(sizeof(SM_EXEC_PGM_MSG) == 0x48);
 
 typedef struct _SM_LOAD_DEFERED_SUBSYSTEM_MSG
 {
diff --git a/reactos/lib/rtl/process.c b/reactos/lib/rtl/process.c
index ae91e2423f7..1a23086d16d 100644
--- a/reactos/lib/rtl/process.c
+++ b/reactos/lib/rtl/process.c
@@ -362,16 +362,19 @@ RtlSetProcessIsCritical(IN BOOLEAN NewValue,
                         OUT PBOOLEAN OldValue OPTIONAL,
                         IN BOOLEAN NeedBreaks)
 {
-    ULONG BreakOnTermination = FALSE;
+    ULONG BreakOnTermination;
 
-    if (OldValue)
-        *OldValue = FALSE;
+    /* Initialize to FALSE */
+    if (OldValue) *OldValue = FALSE;
 
     /* Fail, if the critical breaks flag is required but is not set */
-    if (NeedBreaks == TRUE &&
+    if ((NeedBreaks) &&
         !(NtCurrentPeb()->NtGlobalFlag & FLG_ENABLE_SYSTEM_CRIT_BREAKS))
+    {
         return STATUS_UNSUCCESSFUL;
+    }
 
+    /* Check if the caller wants the old value */
     if (OldValue)
     {
         /* Query and return the old break on termination flag for the process */
diff --git a/reactos/lib/rtl/thread.c b/reactos/lib/rtl/thread.c
index 3213b338e64..717cdb2e45c 100644
--- a/reactos/lib/rtl/thread.c
+++ b/reactos/lib/rtl/thread.c
@@ -150,6 +150,48 @@ RtlpFreeUserStack(IN HANDLE Process,
 
 /* FUNCTIONS ***************************************************************/
 
+
+/*
+ * @implemented
+ */
+NTSTATUS
+NTAPI
+RtlSetThreadIsCritical(IN BOOLEAN NewValue,
+                       OUT PBOOLEAN OldValue OPTIONAL,
+                       IN BOOLEAN NeedBreaks)
+{
+    ULONG BreakOnTermination;
+
+    /* Initialize to FALSE */
+    if (OldValue) *OldValue = FALSE;
+
+    /* Fail, if the critical breaks flag is required but is not set */
+    if ((NeedBreaks) &&
+        !(NtCurrentPeb()->NtGlobalFlag & FLG_ENABLE_SYSTEM_CRIT_BREAKS))
+    {
+        return STATUS_UNSUCCESSFUL;
+    }
+
+    /* Check if the caller wants the old value */
+    if (OldValue)
+    {
+        /* Query and return the old break on termination flag for the process */
+        ZwQueryInformationThread(NtCurrentThread(),
+                                 ThreadBreakOnTermination,
+                                 &BreakOnTermination,
+                                 sizeof(ULONG),
+                                 NULL);
+        *OldValue = (BOOLEAN)BreakOnTermination;
+    }
+
+    /* Set the break on termination flag for the process */
+    BreakOnTermination = NewValue;
+    return ZwSetInformationThread(NtCurrentThread(),
+                                  ThreadBreakOnTermination,
+                                  &BreakOnTermination,
+                                  sizeof(ULONG));
+}
+
 /*
  @implemented
 */