diff --git a/reactos/sdk/include/xdk/rtlfuncs.h b/reactos/sdk/include/xdk/rtlfuncs.h
index 01059d43e50..b3e82b80925 100644
--- a/reactos/sdk/include/xdk/rtlfuncs.h
+++ b/reactos/sdk/include/xdk/rtlfuncs.h
@@ -978,6 +978,18 @@ RtlUnicodeStringToAnsiString(
   _In_ PCUNICODE_STRING SourceString,
   _In_ BOOLEAN AllocateDestinationString);
 
+_IRQL_requires_max_(PASSIVE_LEVEL)
+_Must_inspect_result_
+NTSYSAPI
+NTSTATUS
+NTAPI
+RtlUpcaseUnicodeStringToAnsiString(
+  _When_(AllocateDestinationString, _Out_ _At_(DestinationString->Buffer, __drv_allocatesMem(Mem)))
+  _When_(!AllocateDestinationString, _Inout_)
+    PANSI_STRING DestinationString,
+  _In_ PCUNICODE_STRING SourceString,
+  _In_ BOOLEAN AllocateDestinationString);
+
 _IRQL_requires_max_(PASSIVE_LEVEL)
 NTSYSAPI
 ULONG
diff --git a/reactos/sdk/lib/rtl/unicode.c b/reactos/sdk/lib/rtl/unicode.c
index 99da382ea6e..486bf1d8d89 100644
--- a/reactos/sdk/lib/rtl/unicode.c
+++ b/reactos/sdk/lib/rtl/unicode.c
@@ -1779,7 +1779,7 @@ NTSTATUS
 NTAPI
 RtlUnicodeStringToCountedOemString(
     IN OUT POEM_STRING OemDest,
-    IN PUNICODE_STRING UniSource,
+    IN PCUNICODE_STRING UniSource,
     IN BOOLEAN AllocateDestinationString)
 {
     NTSTATUS Status;
@@ -1942,7 +1942,7 @@ NTSTATUS
 NTAPI
 RtlUpcaseUnicodeStringToAnsiString(
     IN OUT PANSI_STRING AnsiDest,
-    IN PUNICODE_STRING UniSource,
+    IN PCUNICODE_STRING UniSource,
     IN BOOLEAN  AllocateDestinationString)
 {
     NTSTATUS Status;