diff --git a/Library/Homebrew/utils/service.rb b/Library/Homebrew/utils/service.rb
index ceb8cd36e2..3c13d75c70 100644
--- a/Library/Homebrew/utils/service.rb
+++ b/Library/Homebrew/utils/service.rb
@@ -1,4 +1,4 @@
-# typed: true
+# typed: strict
 # frozen_string_literal: true
 
 module Utils
@@ -27,7 +27,7 @@ module Utils
       return @launchctl if defined? @launchctl
       return if ENV["HOMEBREW_TEST_GENERIC_OS"]
 
-      @launchctl = which("launchctl")
+      @launchctl = T.let(which("launchctl"), T.nilable(Pathname))
     end
 
     # Path to systemctl binary.
@@ -36,7 +36,7 @@ module Utils
       return @systemctl if defined? @systemctl
       return if ENV["HOMEBREW_TEST_GENERIC_OS"]
 
-      @systemctl = which("systemctl")
+      @systemctl = T.let(which("systemctl"), T.nilable(Pathname))
     end
 
     sig { returns(T::Boolean) }