diff --git a/R/06-LoadPars.R b/R/06-LoadPars.R
index 1d0698c4..1cdc1995 100644
--- a/R/06-LoadPars.R
+++ b/R/06-LoadPars.R
@@ -277,7 +277,7 @@ LoadPars <- function(itemtype, itemloc, lambdas, zetas, guess, upper, fulldata,
         item_nfi <- ifelse(!is.null(mixed.design) &&
                           mixed.design$has_idesign[i], nfixedeffects, 0)
         item_nfact <- nfact
-        if(!mixed.design$has_idesign[i])
+        if(!is.null(mixed.design) && !mixed.design$has_idesign[i])
             item_nfact <- nfact - nfixedeffects