diff --git a/Library/Homebrew/completions/bash.erb b/Library/Homebrew/completions/bash.erb
index 6bab42bbc6..1cdb120743 100644
--- a/Library/Homebrew/completions/bash.erb
+++ b/Library/Homebrew/completions/bash.erb
@@ -13,6 +13,12 @@
 %>
 # Bash completion script for brew(1)
 
+if test -v POSIXLY_CORRECT || test -o posix 
+then
+  echo "Homebrew Bash completions do not work in POSIX mode" 1>&2
+  return
+fi
+
 __brewcomp_words_include() {
   local element idx 
   for (( idx = 1; idx < COMP_CWORD; idx++ ))
diff --git a/completions/bash/brew b/completions/bash/brew
index 1426bf06ff..3b471f6dcc 100644
--- a/completions/bash/brew
+++ b/completions/bash/brew
@@ -1,5 +1,11 @@
 # Bash completion script for brew(1)
 
+if test -v POSIXLY_CORRECT || test -o posix 
+then
+  echo "Homebrew Bash completions do not work in POSIX mode" 1>&2
+  return
+fi
+
 __brewcomp_words_include() {
   local element idx 
   for (( idx = 1; idx < COMP_CWORD; idx++ ))