diff --git a/Library/Homebrew/dev-cmd/update-test.rb b/Library/Homebrew/dev-cmd/update-test.rb
index e6d09edf565ff..8bb643b21c3fa 100644
--- a/Library/Homebrew/dev-cmd/update-test.rb
+++ b/Library/Homebrew/dev-cmd/update-test.rb
@@ -1,14 +1,12 @@
-# typed: false
+# typed: true
 # frozen_string_literal: true
 
 require "cli/parser"
 module Homebrew
   extend T::Sig
 
-  module_function
-
   sig { returns(CLI::Parser) }
-  def update_test_args
+  def self.update_test_args
     Homebrew::CLI::Parser.new do
       description <<~EOS
         Run a test of `brew update` with a new repository clone.
@@ -27,7 +25,7 @@ def update_test_args
     end
   end
 
-  def update_test
+  def self.update_test
     args = update_test_args.parse
 
     # Avoid `update-report.rb` tapping Homebrew/homebrew-core
@@ -51,10 +49,12 @@ def update_test
       "master"
     end
 
-    start_commit = nil
+    # Utils.popen_read returns a String without a block argument, but that isn't easily typed. We thus label this
+    # as untyped for now.
+    start_commit = T.let("", T.untyped)
     end_commit = "HEAD"
     cd HOMEBREW_REPOSITORY do
-      start_commit = if (commit = args.commit)
+      start_commit = if (commit = T.let(args.commit, T.nilable(String)))
         commit
       elsif (date = args.before)
         Utils.popen_read("git", "rev-list", "-n1", "--before=#{date}", "origin/master").chomp
@@ -78,7 +78,7 @@ def update_test
       start_commit = Utils.popen_read("git", "rev-parse", start_commit).chomp
       odie "Could not find start commit!" if start_commit.empty?
 
-      end_commit = Utils.popen_read("git", "rev-parse", end_commit).chomp
+      end_commit = T.cast(Utils.popen_read("git", "rev-parse", end_commit).chomp, String)
       odie "Could not find end commit!" if end_commit.empty?
 
       if Utils.popen_read("git", "branch", "--list", "master").blank?
@@ -114,7 +114,7 @@ def update_test
       safe_system "git", "reset", "--hard", start_commit
 
       # update ENV["PATH"]
-      ENV["PATH"] = PATH.new(ENV.fetch("PATH")).prepend(curdir/"bin")
+      ENV["PATH"] = PATH.new(ENV.fetch("PATH")).prepend(curdir/"bin").to_s
 
       # run brew help to install portable-ruby (if needed)
       quiet_system "brew", "help"
@@ -139,7 +139,7 @@ def update_test
     FileUtils.rm_rf "update-test" unless args.keep_tmp?
   end
 
-  def git_tags
+  def self.git_tags
     tags = Utils.popen_read("git", "tag", "--list", "--sort=-version:refname")
     if tags.blank?
       tags = if (HOMEBREW_REPOSITORY/".git/shallow").exist?
diff --git a/Library/Homebrew/extend/git_repository.rb b/Library/Homebrew/extend/git_repository.rb
index a91ec91704529..6e21970e31d80 100644
--- a/Library/Homebrew/extend/git_repository.rb
+++ b/Library/Homebrew/extend/git_repository.rb
@@ -117,6 +117,6 @@ def popen_git(*args, safe: false, err: nil)
       raise "Git is unavailable"
     end
 
-    T.unsafe(Utils).popen_read(Utils::Git.git, *args, safe: safe, chdir: self, err: err).chomp.presence
+    Utils.popen_read(Utils::Git.git, *args, safe: safe, chdir: self, err: err).chomp.presence
   end
 end
diff --git a/Library/Homebrew/extend/io.rb b/Library/Homebrew/extend/io.rb
index f5d36dfc84f8b..383b8213c918e 100644
--- a/Library/Homebrew/extend/io.rb
+++ b/Library/Homebrew/extend/io.rb
@@ -1,4 +1,4 @@
-# typed: false
+# typed: true
 # frozen_string_literal: true
 
 class IO
@@ -6,17 +6,19 @@ def readline_nonblock(sep = $INPUT_RECORD_SEPARATOR)
     line = +""
     buffer = +""
 
-    loop do
-      break if buffer == sep
+    begin
+      loop do
+        break if buffer == sep
 
-      read_nonblock(1, buffer)
-      line.concat(buffer)
-    end
+        read_nonblock(1, buffer)
+        line.concat(buffer)
+      end
 
-    line.freeze
-  rescue IO::WaitReadable, EOFError => e
-    raise e if line.empty?
+      line.freeze
+    rescue IO::WaitReadable, EOFError
+      raise if line.empty?
 
-    line.freeze
+      line.freeze
+    end
   end
 end