diff --git a/tools/upgrade.sh b/tools/upgrade.sh
index 34ff3f027..f7a263d66 100755
--- a/tools/upgrade.sh
+++ b/tools/upgrade.sh
@@ -1,4 +1,5 @@
 #!/usr/bin/env zsh
+set +u # disable nounset
 
 local ret=0 # exit code