diff --git a/reactos/dll/win32/user32/misc/rtlstr.c b/reactos/dll/win32/user32/misc/rtlstr.c
new file mode 100644
index 00000000000..ebb8e59fd24
--- /dev/null
+++ b/reactos/dll/win32/user32/misc/rtlstr.c
@@ -0,0 +1,65 @@
+/*
+ * PROJECT:         ReactOS user32.dll
+ * FILE:            lib/user32/misc/rtlstr.c
+ * PURPOSE:         Large Strings
+ * PROGRAMMER:
+ * UPDATE HISTORY:
+ *
+ */
+
+/* INCLUDES ******************************************************************/
+
+#include <user32.h>
+
+#include <wine/debug.h>
+
+WINE_DEFAULT_DEBUG_CHANNEL(user32);
+
+/* FUNCTIONS *****************************************************************/
+VOID
+NTAPI
+RtlInitLargeAnsiString(IN OUT PLARGE_ANSI_STRING DestinationString,
+                       IN PCSZ SourceString,
+                       IN INT Unknown)
+{
+    ULONG DestSize;
+
+    if (SourceString)
+    {
+        DestSize = strlen(SourceString);
+        DestinationString->Length = DestSize;
+        DestinationString->MaximumLength = DestSize + sizeof(CHAR);
+    }
+    else
+    {
+        DestinationString->Length = 0;
+        DestinationString->MaximumLength = 0;
+    }
+
+    DestinationString->Buffer = (PCHAR)SourceString;
+    DestinationString->bAnsi  = TRUE;
+}
+
+VOID
+NTAPI
+RtlInitLargeUnicodeString(IN OUT PLARGE_UNICODE_STRING DestinationString,
+                          IN PCWSTR SourceString,
+                          IN INT Unknown)
+{
+    ULONG DestSize;
+
+    if (SourceString)
+    {
+        DestSize = wcslen(SourceString) * sizeof(WCHAR);
+        DestinationString->Length = DestSize;
+        DestinationString->MaximumLength = DestSize + sizeof(WCHAR);
+    }
+    else
+    {
+        DestinationString->Length = 0;
+        DestinationString->MaximumLength = 0;
+    }
+
+    DestinationString->Buffer = (PWSTR)SourceString;
+    DestinationString->bAnsi  = FALSE;
+}
diff --git a/reactos/dll/win32/user32/user32.rbuild b/reactos/dll/win32/user32/user32.rbuild
index 246b26b1be6..4bc82db5509 100644
--- a/reactos/dll/win32/user32/user32.rbuild
+++ b/reactos/dll/win32/user32/user32.rbuild
@@ -40,6 +40,7 @@
 		<file>misc.c</file>
 		<file>object.c</file>
 		<file>resources.c</file>
+		<file>rtlstr.c</file>
 		<file>stubs.c</file>
 		<file>timer.c</file>
 		<file>winhelp.c</file>
diff --git a/reactos/include/reactos/probe.h b/reactos/include/reactos/probe.h
index a1c22091bf0..2686a20b165 100644
--- a/reactos/include/reactos/probe.h
+++ b/reactos/include/reactos/probe.h
@@ -48,6 +48,7 @@ VOID NTAPI W32kRaiseStatus(NTSTATUS Status);
 #define ProbeForWriteLargeInteger(Ptr) ProbeForWriteGenericType(&((PLARGE_INTEGER)Ptr)->QuadPart, LONGLONG)
 #define ProbeForWriteUlargeInteger(Ptr) ProbeForWriteGenericType(&((PULARGE_INTEGER)Ptr)->QuadPart, ULONGLONG)
 #define ProbeForWriteUnicodeString(Ptr) ProbeForWriteGenericType((PUNICODE_STRING)Ptr, UNICODE_STRING)
+#define ProbeForWriteLargeString(Ptr) ProbeForWriteGenericType((PLARGE_STRING)Ptr, LARGE_STRING)
 #define ProbeForWriteIoStatusBlock(Ptr) ProbeForWriteGenericType((PIO_STATUS_BLOCK)Ptr, IO_STATUS_BLOCK)
 
 #define ProbeForReadGenericType(Ptr, Type, Default)                            \
@@ -74,6 +75,7 @@ VOID NTAPI W32kRaiseStatus(NTSTATUS Status);
 #define ProbeForReadLargeInteger(Ptr) ProbeForReadGenericType((const LARGE_INTEGER *)(Ptr), LARGE_INTEGER, __emptyLargeInteger)
 #define ProbeForReadUlargeInteger(Ptr) ProbeForReadGenericType((const ULARGE_INTEGER *)(Ptr), ULARGE_INTEGER, __emptyULargeInteger)
 #define ProbeForReadUnicodeString(Ptr) ProbeForReadGenericType((const UNICODE_STRING *)(Ptr), UNICODE_STRING, __emptyUnicodeString)
+#define ProbeForReadLargeString(Ptr) ProbeForReadGenericType((const LARGE_STRING *)(Ptr), LARGE_STRING, __emptyLargeString)
 #define ProbeForReadIoStatusBlock(Ptr) ProbeForReadGenericType((const IO_STATUS_BLOCK *)(Ptr), IO_STATUS_BLOCK, __emptyIoStatusBlock)
 
 #define ProbeAndZeroHandle(Ptr) \
diff --git a/reactos/include/reactos/win32k/ntuser.h b/reactos/include/reactos/win32k/ntuser.h
index 90fe7f2d152..ed0c85f0226 100644
--- a/reactos/include/reactos/win32k/ntuser.h
+++ b/reactos/include/reactos/win32k/ntuser.h
@@ -5,6 +5,36 @@ struct _W32PROCESSINFO;
 struct _W32THREADINFO;
 struct _WINDOW;
 
+typedef struct _LARGE_UNICODE_STRING
+{
+  ULONG Length;
+  ULONG MaximumLength:31;
+  ULONG bAnsi:1;
+  PWSTR Buffer;
+} LARGE_UNICODE_STRING, *PLARGE_UNICODE_STRING;
+
+typedef struct _LARGE_STRING
+{
+  ULONG Length;
+  ULONG MaximumLength:31;
+  ULONG bAnsi:1;
+  PVOID Buffer;
+} LARGE_STRING, *PLARGE_STRING;
+//
+// Based on ANSI_STRING
+//
+typedef struct _LARGE_ANSI_STRING
+{
+  ULONG Length;
+  ULONG MaximumLength:31;
+  ULONG bAnsi:1;
+  PCHAR Buffer;
+} LARGE_ANSI_STRING, *PLARGE_ANSI_STRING;
+
+VOID NTAPI RtlInitLargeAnsiString(IN OUT PLARGE_ANSI_STRING,IN PCSZ,IN INT);
+VOID NTAPI RtlInitLargeUnicodeString(IN OUT PLARGE_UNICODE_STRING,IN PCWSTR,IN INT);
+
+
 /* FIXME: UserHMGetHandle needs to be updated once the new handle manager is implemented */
 #define UserHMGetHandle(obj) ((obj)->hdr.Handle)
 
@@ -1086,9 +1116,9 @@ HWND
 NTAPI
 NtUserCreateWindowEx(
   DWORD dwExStyle,
-  PLARGE_UNICODE_STRING plustrClassName,
-  PLARGE_UNICODE_STRING plustrClsVesrion,
-  PLARGE_UNICODE_STRING plustrWindowName,
+  PLARGE_STRING plstrClassName,
+  PLARGE_STRING plstrClsVesrion,
+  PLARGE_STRING plstrWindowName,
   DWORD dwStyle,
   int x,
   int y,