diff --git a/DESCRIPTION b/DESCRIPTION
index 75019eb..61b7acb 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -41,3 +41,5 @@ VignetteBuilder: knitr
 RoxygenNote: 7.3.0
 Encoding: UTF-8
 BugReports: https://github.com/jknowles/merTools
+Config/testthat/edition: 3
+Config/testthat/parallel: true
diff --git a/NEWS.md b/NEWS.md
index dde677b..03f534f 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -3,6 +3,7 @@
 ## merTools 0.6.2
 
 - Maintenance release to fix minor issues with function documentation
+- Fix #130 by avoiding conflict with `vcov` in the `merDeriv` package
 
 ## merTools 0.6.1
 
diff --git a/R/merFastDisplay.R b/R/merFastDisplay.R
index 480f473..3a8dd06 100644
--- a/R/merFastDisplay.R
+++ b/R/merFastDisplay.R
@@ -37,7 +37,7 @@ fastdisp.merMod <- function (x, ...)
     print(out$call)
     fcoef <- fixef(x)
     useScale <- getME(x, "devcomp")$dims["useSc"]
-    corF <- vcov(x)@factors$correlation
+    corF <- lme4::vcov.merMod(x)@factors$correlation
     coefs <- cbind(fcoef, corF@sd)
     if (length(fcoef) > 0) {
       if (!useScale) {