diff --git a/Library/Homebrew/os/mac/sdk.rb b/Library/Homebrew/os/mac/sdk.rb
index 4b6f893efb..f39d9e527d 100644
--- a/Library/Homebrew/os/mac/sdk.rb
+++ b/Library/Homebrew/os/mac/sdk.rb
@@ -9,6 +9,8 @@ module OS
     #
     # @api private
     class SDK
+      VERSIONED_SDK_REGEX = /MacOSX(\d+\.\d+)\.sdk$/.freeze
+
       attr_reader :version, :path, :source
 
       def initialize(version, path, source)
@@ -25,14 +27,39 @@ module OS
       class NoSDKError < StandardError; end
 
       def sdk_for(v)
-        path = sdk_paths[v]
-        raise NoSDKError if path.nil?
+        sdk = all_sdks.find { |s| s.version == v }
+        raise NoSDKError if sdk.nil?
 
-        SDK.new v, path, source
+        sdk
       end
 
       def all_sdks
-        sdk_paths.map { |v, p| SDK.new v, p, source }
+        return @all_sdks if @all_sdks
+
+        @all_sdks = []
+
+        # Bail out if there is no SDK prefix at all
+        return @all_sdks unless File.directory? sdk_prefix
+
+        # Use unversioned SDK path on Big Sur to avoid issues such as:
+        # https://github.com/Homebrew/homebrew-core/issues/67075
+        unversioned_sdk_path = Pathname.new("#{sdk_prefix}/MacOSX.sdk")
+        version = read_sdk_version(unversioned_sdk_path)
+        if version && version >= :big_sur
+          unversioned_sdk_version = version
+          @all_sdks << SDK.new(unversioned_sdk_version, unversioned_sdk_path, source)
+        end
+
+        Dir["#{sdk_prefix}/MacOSX*.sdk"].each do |sdk_path|
+          next unless sdk_path.match?(SDK::VERSIONED_SDK_REGEX)
+
+          version = read_sdk_version(Pathname.new(sdk_path))
+          next if version.nil? || version == unversioned_sdk_version
+
+          @all_sdks << SDK.new(version, sdk_path, source)
+        end
+
+        @all_sdks
       end
 
       def sdk_if_applicable(v = nil)
@@ -64,43 +91,34 @@ module OS
         ""
       end
 
-      def sdk_paths
-        @sdk_paths ||= begin
-          # Bail out if there is no SDK prefix at all
-          if File.directory? sdk_prefix
-            paths = {}
-
-            Dir[File.join(sdk_prefix, "MacOSX*.sdk")].each do |sdk_path|
-              version = sdk_path[/MacOSX(\d+\.\d+)u?\.sdk$/, 1]
-              paths[OS::Mac::Version.new(version)] = sdk_path if version.present?
-            end
-
-            # Use unversioned SDK path on Big Sur to avoid issues such as:
-            # https://github.com/Homebrew/homebrew-core/issues/67075
-            # This creates an entry in `paths` whose key is the OS major version
-            sdk_path = Pathname.new("#{sdk_prefix}/MacOSX.sdk")
-            sdk_settings = sdk_path/"SDKSettings.json"
-            if sdk_settings.exist? &&
-               (sdk_settings_string = sdk_settings.read.presence) &&
-               (sdk_settings_json = JSON.parse(sdk_settings_string).presence) &&
-               (version_string = sdk_settings_json.fetch("Version", nil).presence) &&
-               (version = version_string[/(\d+)\./, 1].presence)
-              paths[OS::Mac::Version.new(version)] = sdk_path
-            end
-
-            paths
-          else
-            {}
-          end
-        end
+      def latest_sdk
+        all_sdks.max_by(&:version)
       end
 
-      # NOTE: This returns a versioned SDK path, even on Big Sur
-      def latest_sdk
-        return if sdk_paths.empty?
+      def read_sdk_version(sdk_path)
+        sdk_settings = sdk_path/"SDKSettings.json"
+        sdk_settings_string = sdk_settings.read if sdk_settings.exist?
 
-        v, path = sdk_paths.max { |(v1, _), (v2, _)| v1 <=> v2 }
-        SDK.new v, path, source
+        # Pre-10.14 SDKs
+        sdk_settings = sdk_path/"SDKSettings.plist"
+        if sdk_settings_string.blank? && sdk_settings.exist?
+          result = system_command("plutil", args: ["-convert", "json", "-o", "-", sdk_settings])
+          sdk_settings_string = result.stdout if result.success?
+        end
+
+        return if sdk_settings_string.blank?
+
+        sdk_settings_json = JSON.parse(sdk_settings_string)
+        return if sdk_settings_json.blank?
+
+        version_string = sdk_settings_json.fetch("Version", nil)
+        return if version_string.blank?
+
+        begin
+          OS::Mac::Version.new(version_string).strip_patch
+        rescue MacOSVersionError
+          nil
+        end
       end
     end
     private_constant :BaseSDKLocator