diff --git a/Library/Homebrew/cask/lib/hbc/pkg.rb b/Library/Homebrew/cask/lib/hbc/pkg.rb
index 7f187c9de0..7d4a9251ab 100644
--- a/Library/Homebrew/cask/lib/hbc/pkg.rb
+++ b/Library/Homebrew/cask/lib/hbc/pkg.rb
@@ -76,7 +76,7 @@ module Hbc
     end
 
     def _with_full_permissions(path)
-      original_mode = (path.stat.mode % 0o1000).to_s(8)
+      original_mode = (path.stat.mode % 01000).to_s(8)
       # TODO: similarly read and restore macOS flags (cf man chflags)
       @command.run!("/bin/chmod", args: ["--", "777", path], sudo: true)
       yield
diff --git a/Library/Homebrew/cask/test/cask/pkg_test.rb b/Library/Homebrew/cask/test/cask/pkg_test.rb
index 5734a58f6a..85a42356e2 100644
--- a/Library/Homebrew/cask/test/cask/pkg_test.rb
+++ b/Library/Homebrew/cask/test/cask/pkg_test.rb
@@ -75,7 +75,7 @@ describe Hbc::Pkg do
 
       fake_file = fake_dir.join("ima_installed_file").tap { |path| FileUtils.touch(path) }
 
-      fake_dir.chmod(0o000)
+      fake_dir.chmod(0000)
 
       pkg.stubs(:pkgutil_bom_specials).returns([])
       pkg.stubs(:pkgutil_bom_files).returns([fake_file])
@@ -88,7 +88,7 @@ describe Hbc::Pkg do
 
       fake_dir.must_be :directory?
       fake_file.wont_be :file?
-      (fake_dir.stat.mode % 0o1000).to_s(8).must_equal "0"
+      (fake_dir.stat.mode % 01000).to_s(8).must_equal "0"
     end
   end
 end