diff --git a/Library/Homebrew/dev-cmd/tests.rb b/Library/Homebrew/dev-cmd/tests.rb
index b0868a87fe..2f293aead9 100644
--- a/Library/Homebrew/dev-cmd/tests.rb
+++ b/Library/Homebrew/dev-cmd/tests.rb
@@ -107,6 +107,14 @@ module Homebrew
         ENV.delete(env)
       end
 
+      # Codespaces /tmp is mounted 755 which makes Ruby warn constantly.
+      if (ENV["HOMEBREW_CODESPACES"] == "true") && (HOMEBREW_TEMP.to_s == "/tmp")
+        homebrew_prefix_tmp = "#{HOMEBREW_PREFIX}/tmp"
+        ENV["HOMEBREW_TEMP"] = homebrew_prefix_tmp
+        FileUtils.mkdir_p homebrew_prefix_tmp
+        system "chmod", "-R", "g-w,o-w", "/tmp"
+      end
+
       ENV["HOMEBREW_NO_ANALYTICS_THIS_RUN"] = "1"
       ENV["HOMEBREW_NO_COMPAT"] = "1" if args.no_compat?
       ENV["HOMEBREW_TEST_GENERIC_OS"] = "1" if args.generic?
diff --git a/bin/brew b/bin/brew
index bfb14ca09b..4725cb6d3d 100755
--- a/bin/brew
+++ b/bin/brew
@@ -84,7 +84,7 @@ HOMEBREW_LIBRARY="${HOMEBREW_REPOSITORY}/Library"
 
 # Copy and export all HOMEBREW_* variables previously mentioned in
 # manpage or used elsewhere by Homebrew.
-for VAR in BAT_THEME BROWSER DISPLAY EDITOR NO_COLOR TMUX DBUS_SESSION_BUS_ADDRESS XDG_RUNTIME_DIR
+for VAR in BAT_THEME BROWSER DISPLAY EDITOR NO_COLOR TMUX DBUS_SESSION_BUS_ADDRESS XDG_RUNTIME_DIR CODESPACES
 do
   # Skip if variable value is empty.
   [[ -z "${!VAR}" ]] && continue