diff --git a/reactos/include/psdk/winnls.h b/reactos/include/psdk/winnls.h
index f3f1cba66db..be2c34e346a 100644
--- a/reactos/include/psdk/winnls.h
+++ b/reactos/include/psdk/winnls.h
@@ -846,6 +846,29 @@ int WINAPI GetTimeFormatW(LCID,DWORD,const SYSTEMTIME*,LPCWSTR,LPWSTR,int);
 LANGID WINAPI GetUserDefaultLangID(void);
 LCID WINAPI GetUserDefaultLCID(void);
 GEOID WINAPI GetUserGeoID(_In_ GEOCLASS);
+
+#if (WINVER >= 0x0600)
+
+int
+WINAPI
+IdnToAscii(
+  _In_ DWORD dwFlags,
+  _In_reads_(cchUnicodeChar) LPCWSTR lpUnicodeCharStr,
+  _In_ int cchUnicodeChar,
+  _Out_writes_opt_(cchASCIIChar) LPWSTR lpASCIICharStr,
+  _In_ int cchASCIIChar);
+
+int
+WINAPI
+IdnToUnicode(
+  _In_ DWORD dwFlags,
+  _In_reads_(cchASCIIChar) LPCWSTR lpASCIICharStr,
+  _In_ int cchASCIIChar,
+  _Out_writes_opt_(cchUnicodeChar) LPWSTR lpUnicodeCharStr,
+  _In_ int cchUnicodeChar);
+
+#endif /* WINVER >= 0x0600 */
+
 BOOL WINAPI IsDBCSLeadByte(_In_ BYTE);
 BOOL WINAPI IsDBCSLeadByteEx(_In_ UINT, _In_ BYTE);