diff --git a/Library/Homebrew/github_runner_matrix.rb b/Library/Homebrew/github_runner_matrix.rb
index fea3c827b2..ed82b51719 100644
--- a/Library/Homebrew/github_runner_matrix.rb
+++ b/Library/Homebrew/github_runner_matrix.rb
@@ -142,7 +142,7 @@ class GitHubRunnerMatrix
       runner, timeout = if use_github_runner && github_runner_available
         ["macos-#{version}", GITHUB_ACTIONS_RUNNER_TIMEOUT]
       else
-        ["#{version}#{ephemeral_suffix}", runner_timeout]
+        ["#{version}-x86_64#{ephemeral_suffix}", runner_timeout]
       end
 
       # macOS 12-x86_64 is usually slower.
diff --git a/Library/Homebrew/test/dev-cmd/determine-test-runners_spec.rb b/Library/Homebrew/test/dev-cmd/determine-test-runners_spec.rb
index ed6b374b37..75125ecfb2 100644
--- a/Library/Homebrew/test/dev-cmd/determine-test-runners_spec.rb
+++ b/Library/Homebrew/test/dev-cmd/determine-test-runners_spec.rb
@@ -33,7 +33,7 @@ RSpec.describe Homebrew::DevCmd::DetermineTestRunners do
       macos_version = MacOSVersion.new(v)
       next if macos_version.unsupported_release?
 
-      out << v
+      out << "#{v}-x86_64"
       out << "#{v}-arm64"
     end