diff --git a/support/update-rundk.sh b/support/update-rundk.sh
index a30d3da..544e4cf 100755
--- a/support/update-rundk.sh
+++ b/support/update-rundk.sh
@@ -72,7 +72,7 @@ fi
 rsync -lpt "$MYDIR/Dockerfile.rundk" "$rundir/"
 
 if [ -n "$projdir" ]; then
-    if should_update "$rundir/build" "$MYDIR/build"; then
+    if testdiff "$rundir/build" "$MYDIR/build"; then
         cp "$MYDIR/build" "$rundir/build"
         chmod +x "$rundir/build"
     fi