diff --git a/tools/build-world.sh b/tools/build-world.sh
index 5cfe6842c4cacd08f9123da973bfd7eb24c9b1bd..9a76e10435e3384262b4863774d1c95a59420c10 100755
--- a/tools/build-world.sh
+++ b/tools/build-world.sh
@@ -43,7 +43,7 @@ $LISP "$@" -noinit -nositeinit <<EOF
 (comf "target:tools/setup" :load t)
 
 (setq *gc-verbose* nil)
-(setq *interactive* ${INTERACTIVE-:nil})
+(setq *interactive* ${INTERACTIVE:-nil})
 (setq debug:*debug-print-level* nil)
 (setq debug:*debug-print-length* nil)