diff --git a/completions/bash/brew b/completions/bash/brew
index 8c50b4be3c..ab3c10eb11 100644
--- a/completions/bash/brew
+++ b/completions/bash/brew
@@ -9,7 +9,7 @@ then
 fi
 
 __brewcomp_words_include() {
-  local element idx 
+  local element idx
   for (( idx = 1; idx < COMP_CWORD; idx++ ))
   do
     element=${COMP_WORDS[idx]}
@@ -75,7 +75,7 @@ __brew_complete_outdated_formulae() {
 __brew_complete_outdated_casks() {
   local cur="${COMP_WORDS[COMP_CWORD]}"
   local outdated_casks
-  outdated_casks="$(brew outdated --cask --quiet)"
+  outdated_casks="$(brew outdated --cask --quiet 2>/dev/null)"
   while read -r line; do COMPREPLY+=("${line}"); done < <(compgen -W "${outdated_casks}" -- "${cur}")
 }
 
diff --git a/completions/zsh/_brew b/completions/zsh/_brew
index 9b2ea9ff20..42d396abdc 100644
--- a/completions/zsh/_brew
+++ b/completions/zsh/_brew
@@ -102,7 +102,7 @@ __brew_installed_casks() {
 
   local -a list
   local expl
-  list=( $(brew list --cask) )
+  list=( $(brew list --cask 2>/dev/null) )
   _wanted list expl 'installed casks' compadd -a list
 }
 
@@ -110,7 +110,7 @@ __brew_outdated_casks() {
   [[ -prefix '-' ]] && return 0
 
   local -a casks
-  casks=($(brew outdated --cask))
+  casks=($(brew outdated --cask 2>/dev/null))
   _describe -t casks 'outdated casks' casks
 }