diff --git a/completions/fish/brew.fish b/completions/fish/brew.fish
index 188a4b9f94..c281613236 100644
--- a/completions/fish/brew.fish
+++ b/completions/fish/brew.fish
@@ -615,7 +615,7 @@ __fish_brew_complete_arg 'desc; and not __fish_seen_argument -l formula -l formu
 
 __fish_brew_complete_cmd 'determine-test-runners' 'Determines the runners used to test formulae or their dependents'
 __fish_brew_complete_arg 'determine-test-runners' -l debug -d 'Display any debugging information'
-__fish_brew_complete_arg 'determine-test-runners' -l dependents -d 'Determine runners for testing dependents'
+__fish_brew_complete_arg 'determine-test-runners' -l dependents -d 'Determine runners for testing dependents. (requires Linux)'
 __fish_brew_complete_arg 'determine-test-runners' -l help -d 'Show this message'
 __fish_brew_complete_arg 'determine-test-runners' -l quiet -d 'Make some output more quiet'
 __fish_brew_complete_arg 'determine-test-runners' -l verbose -d 'Make some output more verbose'
diff --git a/completions/zsh/_brew b/completions/zsh/_brew
index 6e36809e5f..7e1624332a 100644
--- a/completions/zsh/_brew
+++ b/completions/zsh/_brew
@@ -760,7 +760,7 @@ _brew_desc() {
 _brew_determine_test_runners() {
   _arguments \
     '--debug[Display any debugging information]' \
-    '--dependents[Determine runners for testing dependents]' \
+    '--dependents[Determine runners for testing dependents. (requires Linux)]' \
     '--help[Show this message]' \
     '--quiet[Make some output more quiet]' \
     '--verbose[Make some output more verbose]'