diff --git a/hw/uefi/var-service-vars.c b/hw/uefi/var-service-vars.c
index 8533533ea5..5607763525 100644
--- a/hw/uefi/var-service-vars.c
+++ b/hw/uefi/var-service-vars.c
@@ -592,7 +592,7 @@ uefi_vars_mm_get_payload_size(uefi_vars_state *uv, mm_header *mhdr,
         return uefi_vars_mm_error(mhdr, mvar, EFI_BAD_BUFFER_SIZE);
     }
 
-    ps->payload_size = uv->buf_size;
+    ps->payload_size = uv->buf_size - sizeof(*mhdr) - sizeof(*mvar);
     mvar->status = EFI_SUCCESS;
     return length;
 }