=== modified file 'common.zsh'
--- common.zsh	2017-11-30 18:56:11 +0000
+++ common.zsh	2017-11-30 18:51:45 +0000
@@ -158,7 +158,7 @@
 			if [[ "$arg" != *=* ]]; then
 				die "Malformed argument: ${(qqq)arg}"
 			fi
-			if (( $+lift_vars[${arg%%=*}] )); then
+			if (( $+vars[${arg%%=*}] )); then
 				die "Duplicate argument: ${arg%%=*}"
 			fi
 			lift_vars[${arg%%=*}]=${arg#*=}