diff --git a/reactos/lib/rtl/sd.c b/reactos/lib/rtl/sd.c
index 772fc01c94d..a332b98e5b1 100644
--- a/reactos/lib/rtl/sd.c
+++ b/reactos/lib/rtl/sd.c
@@ -455,6 +455,7 @@ RtlMakeSelfRelativeSD(PISECURITY_DESCRIPTOR AbsSD,
    TotalLength = sizeof(SECURITY_DESCRIPTOR_RELATIVE) + OwnerLength + GroupLength + SaclLength + DaclLength;
    if (*BufferLength < TotalLength)
    {
+      *BufferLength = TotalLength;
       return STATUS_BUFFER_TOO_SMALL;
    }