diff --git a/Library/Homebrew/dev-cmd/sh.rb b/Library/Homebrew/dev-cmd/sh.rb
index f9285459f9..d1eaf4c812 100644
--- a/Library/Homebrew/dev-cmd/sh.rb
+++ b/Library/Homebrew/dev-cmd/sh.rb
@@ -44,16 +44,18 @@ module Homebrew
     ENV["VERBOSE"] = "1" if args.verbose?
 
     if args.cmd.present?
-      safe_system(ENV["SHELL"], "-c", args.cmd)
+      safe_system(preferred_shell, "-c", args.cmd)
     elsif args.named.present?
-      safe_system(ENV["SHELL"], args.named.first)
+      safe_system(preferred_shell, args.named.first)
     else
-      subshell = if ENV["SHELL"].include?("zsh")
-        "PS1='brew %B%F{green}%~%f%b$ ' #{ENV["SHELL"]} -d -f"
-      elsif ENV["SHELL"].include?("bash")
-        "PS1=\"brew \\[\\033[1;32m\\]\\w\\[\\033[0m\\]$ \" #{ENV["SHELL"]} --noprofile --norc"
+      shell_type = Utils::Shell.preferred
+      subshell = case shell_type
+      when :zsh
+        "PS1='brew %B%F{green}%~%f%b$ ' #{preferred_shell} -d -f"
+      when :bash
+        "PS1=\"brew \\[\\033[1;32m\\]\\w\\[\\033[0m\\]$ \" #{preferred_shell} --noprofile --norc"
       else
-        "PS1=\"brew \\[\\033[1;32m\\]\\w\\[\\033[0m\\]$ \" #{ENV["SHELL"]}"
+        "PS1=\"brew \\[\\033[1;32m\\]\\w\\[\\033[0m\\]$ \" #{preferred_shell}"
       end
       puts <<~EOS
         Your shell has been configured to use Homebrew's build environment;
diff --git a/Library/Homebrew/utils.rb b/Library/Homebrew/utils.rb
index 126a11544c..dfe5ceb7f2 100644
--- a/Library/Homebrew/utils.rb
+++ b/Library/Homebrew/utils.rb
@@ -291,12 +291,12 @@ module Kernel
       ENV["HOMEBREW_DEBUG_INSTALL"] = f.full_name
     end
 
-    if ENV["SHELL"].include?("zsh") && (home = Dir.home).start_with?(HOMEBREW_TEMP.resolved_path.to_s)
+    if Utils::Shell.preferred == :zsh && (home = Dir.home).start_with?(HOMEBREW_TEMP.resolved_path.to_s)
       FileUtils.mkdir_p home
       FileUtils.touch "#{home}/.zshrc"
     end
 
-    Process.wait fork { exec ENV.fetch("SHELL") }
+    Process.wait fork { exec preferred_shell }
 
     return if $CHILD_STATUS.success?
     raise "Aborted due to non-zero exit status (#{$CHILD_STATUS.exitstatus})" if $CHILD_STATUS.exited?
@@ -608,6 +608,11 @@ module Kernel
     end
   end
 
+  sig { returns(String) }
+  def preferred_shell
+    ENV.fetch("SHELL", "/bin/sh")
+  end
+
   sig { returns(String) }
   def shell_profile
     Utils::Shell.profile