diff --git a/dlls/ntdll/unix/env.c b/dlls/ntdll/unix/env.c
index ee958ae71f4..5b192f39732 100644
--- a/dlls/ntdll/unix/env.c
+++ b/dlls/ntdll/unix/env.c
@@ -2356,6 +2356,15 @@ NTSTATUS WINAPI RtlUnicodeToUTF8N( char *dst, DWORD dstlen, DWORD *reslen, const
     return status;
 }
 
+/**********************************************************************
+ *      RtlInitUnicodeString  (ntdll.so)
+ */
+void WINAPI RtlInitUnicodeString( UNICODE_STRING *str, const WCHAR *data )
+{
+    if (data) init_unicode_string( str, data );
+    else str->Length = str->MaximumLength = 0;
+}
+
 /**********************************************************************
  *      RtlNtStatusToDosError  (ntdll.so)
  */