diff --git a/Library/Homebrew/completions/bash.erb b/Library/Homebrew/completions/bash.erb
index 936bdd3abc..d86e0f4b50 100644
--- a/Library/Homebrew/completions/bash.erb
+++ b/Library/Homebrew/completions/bash.erb
@@ -15,7 +15,7 @@
 # This file is automatically generated by running `brew generate-man-completions`.
 # See Library/Homebrew/completions/bash.erb for editing instructions.
 
-if [[ -n ${POSIXLY_CORRECT} ]] || shopt -oq posix
+if [[ -n ${POSIXLY_CORRECT:-} ]] || shopt -oq posix
 then
   echo "Homebrew Bash completions do not work in POSIX mode" 1>&2
   return