diff --git a/Library/Homebrew/utils/inreplace.rb b/Library/Homebrew/utils/inreplace.rb
index b7e625b6ea..6cb8c25729 100644
--- a/Library/Homebrew/utils/inreplace.rb
+++ b/Library/Homebrew/utils/inreplace.rb
@@ -47,6 +47,7 @@ module Utils
     }
     def inreplace(paths, before = nil, after = nil, audit_result = true) # rubocop:disable Style/OptionalBooleanParameter
       after &&= after.to_s
+      before = before.to_s if before.is_a?(Pathname)
 
       errors = {}
 
@@ -59,7 +60,7 @@ module Utils
         if before.nil? && after.nil?
           yield s
         else
-          s.gsub!(T.must(before), after, audit_result)
+          s.gsub!(T.must(before), T.must(after), audit_result)
         end
 
         errors[path] = s.errors unless s.errors.empty?
diff --git a/Library/Homebrew/utils/string_inreplace_extension.rb b/Library/Homebrew/utils/string_inreplace_extension.rb
index 6288089891..8c5c49dc10 100644
--- a/Library/Homebrew/utils/string_inreplace_extension.rb
+++ b/Library/Homebrew/utils/string_inreplace_extension.rb
@@ -1,16 +1,20 @@
-# typed: true
+# typed: strict
 # frozen_string_literal: true
 
 # Used by the `inreplace` function (in `utils.rb`).
 #
 # @api private
 class StringInreplaceExtension
-  attr_accessor :errors, :inreplace_string
+  sig { returns(T::Array[String]) }
+  attr_accessor :errors
+
+  sig { returns(String) }
+  attr_accessor :inreplace_string
 
   sig { params(string: String).void }
   def initialize(string)
     @inreplace_string = string
-    @errors = []
+    @errors = T.let([], T::Array[String])
   end
 
   # Same as `String#sub!`, but warns if nothing was replaced.
@@ -27,7 +31,7 @@ class StringInreplaceExtension
   #
   # @api public
   sig {
-    params(before: T.any(Pathname, Regexp, String), after: T.nilable(String), audit_result: T::Boolean)
+    params(before: T.any(Regexp, String), after: String, audit_result: T::Boolean)
       .returns(T.nilable(String))
   }
   def gsub!(before, after, audit_result = true) # rubocop:disable Style/OptionalBooleanParameter
@@ -65,6 +69,6 @@ class StringInreplaceExtension
   # @api public
   sig { params(flag: String).returns(String) }
   def get_make_var(flag)
-    inreplace_string[/^#{Regexp.escape(flag)}[ \t]*[\\?+:!]?=[ \t]*((?:.*\\\n)*.*)$/, 1]
+    T.must(inreplace_string[/^#{Regexp.escape(flag)}[ \t]*[\\?+:!]?=[ \t]*((?:.*\\\n)*.*)$/, 1])
   end
 end