diff --git a/R/modsem_mplus.R b/R/modsem_mplus.R
index bc15bced..1f9e9bab 100644
--- a/R/modsem_mplus.R
+++ b/R/modsem_mplus.R
@@ -725,9 +725,9 @@ cleanupMplusFiles <- function(fprefix) {
 }
 
 
-getMplusFilePrefix <- function(max.iter = 20) {
+getMplusFilePrefix <- function(max.iter = 20, base = "mpresults") {
   randid <- generateRandomCharId(n=12)
-  fprefix <- paste0("mplusResults", randid)
+  fprefix <- paste0(base, randid)
 
   if (!mplusFilePrefixExists(fprefix))
     return(fprefix)
@@ -747,3 +747,12 @@ getMplusFilePrefix <- function(max.iter = 20) {
 
   fprefix
 }
+
+
+generateRandomCharId <- function(n = 36) {
+  # use only lower letters, as Mplus sometimes seem to convert upper case
+  # characters in the .inp file to lower characters in the .out file. In
+  # particular this seems to happen on Mplus 8.11 on Windows
+  chars <- c(letters, as.character(0:9))
+  paste0(sample(chars, size = n, replace = TRUE), collapse = "")
+}
diff --git a/R/utils.R b/R/utils.R
index bedf3c0f..89768740 100644
--- a/R/utils.R
+++ b/R/utils.R
@@ -848,9 +848,3 @@ std1 <- function(v) {
 
   (v - mu) / sigma
 }
-
-
-generateRandomCharId <- function(n = 36) {
-  chars <- c(letters, LETTERS, as.character(0:9))
-  paste0(sample(chars, size = n, replace = TRUE), collapse = "")
-}