diff --git a/cmd/run.go b/cmd/run.go
index 01c51130..52233852 100644
--- a/cmd/run.go
+++ b/cmd/run.go
@@ -353,7 +353,7 @@ func (r *Runner) Run(ctx context.Context, patterns []string) error {
 		if r.config.DirName != "" {
 			r.program, err = sdkbuild.RubyProgramFromDir(
 				filepath.Join(r.rootDir, r.config.DirName),
-				r.rootDir,
+				filepath.Join(r.rootDir, "harness", "ruby"),
 			)
 		}
 		if err == nil {
diff --git a/cmd/run_ruby.go b/cmd/run_ruby.go
index adc2142e..e0fe46d8 100644
--- a/cmd/run_ruby.go
+++ b/cmd/run_ruby.go
@@ -20,9 +20,10 @@ func (p *Preparer) BuildRubyProgram(ctx context.Context) (sdkbuild.Program, erro
 	// Get version from harness/ruby/Gemfile if not present.
 	// If no version constraint is specified in the Gemfile, version stays empty
 	// and the package manager will resolve to the latest release.
+	rubyDir := filepath.Join(p.rootDir, "harness", "ruby")
 	version := p.config.Version
 	if version == "" {
-		b, err := os.ReadFile(filepath.Join(p.rootDir, "harness", "ruby", "Gemfile"))
+		b, err := os.ReadFile(filepath.Join(rubyDir, "Gemfile"))
 		if err != nil {
 			return nil, fmt.Errorf("failed reading harness/ruby/Gemfile: %w", err)
 		}
@@ -41,9 +42,10 @@ func (p *Preparer) BuildRubyProgram(ctx context.Context) (sdkbuild.Program, erro
 	}
 
 	prog, err := sdkbuild.BuildRubyProgram(ctx, sdkbuild.BuildRubyProgramOptions{
-		BaseDir: p.rootDir,
-		DirName: p.config.DirName,
-		Version: version,
+		BaseDir:   p.rootDir,
+		SourceDir: rubyDir,
+		DirName:   p.config.DirName,
+		Version:   version,
 	})
 	if err != nil {
 		return nil, fmt.Errorf("failed preparing: %w", err)
diff --git a/sdkbuild/ruby.go b/sdkbuild/ruby.go
index 5a2eacc6..6390d91d 100644
--- a/sdkbuild/ruby.go
+++ b/sdkbuild/ruby.go
@@ -14,6 +14,8 @@ import (
 type BuildRubyProgramOptions struct {
 	// Directory that will have a temporary directory created underneath.
 	BaseDir string
+	// Directory containing the Ruby source (gemspec + runner.rb).
+	SourceDir string
 	// If not set, no version constraint is applied and the package manager
 	// resolves to the latest release. If it contains a slash it is assumed
 	// to be a path to the Ruby SDK repo. Otherwise it is a specific version
@@ -42,7 +44,7 @@ func BuildRubyProgram(ctx context.Context, options BuildRubyProgramOptions) (*Ru
 		return nil, fmt.Errorf("base dir required")
 	}
 
-	sourceDir := filepath.Join(options.BaseDir, "harness", "ruby")
+	sourceDir := options.SourceDir
 
 	// Create temp dir if needed that we will remove if creating is unsuccessful
 	success := false
@@ -74,7 +76,9 @@ func BuildRubyProgram(ctx context.Context, options BuildRubyProgramOptions) (*Ru
 		return cmd.Run()
 	}
 
-	// Build the Gemfile content
+	// Build the Gemfile content. We use Bundler's `gemspec` directive to
+	// auto-discover the gemspec in the source directory (via path: option).
+	// This works for any gem name (harness, omes, etc.).
 	var gemfileContent string
 	if strings.ContainsAny(options.Version, `/\`) {
 		// It's a path to a local SDK repo
@@ -94,21 +98,20 @@ func BuildRubyProgram(ctx context.Context, options BuildRubyProgramOptions) (*Ru
 		gemfileContent = fmt.Sprintf(`source "https://rubygems.org"
 
 gem "temporalio", path: %q
-gem "harness", path: %q
+gemspec path: %q
 `, gemPath, sourceDir)
 	} else if options.Version != "" {
 		version := strings.TrimPrefix(options.Version, "v")
 		gemfileContent = fmt.Sprintf(`source "https://rubygems.org"
 
 gem "temporalio", "%s"
-gem "harness", path: %q
+gemspec path: %q
 `, version, sourceDir)
 	} else {
 		// No version constraint — Bundler resolves to latest from RubyGems
 		gemfileContent = fmt.Sprintf(`source "https://rubygems.org"
 
-gem "temporalio"
-gem "harness", path: %q
+gemspec path: %q
 `, sourceDir)
 	}
 
@@ -155,13 +158,13 @@ gem "harness", path: %q
 }
 
 // RubyProgramFromDir recreates the Ruby program from a Dir() result of a
-// BuildRubyProgram(). Note, the base directory of dir when it was built must
-// also be present.
-func RubyProgramFromDir(dir string, rootDir string) (*RubyProgram, error) {
+// BuildRubyProgram(). The sourceDir should point to the directory containing
+// the gemspec and runner.rb.
+func RubyProgramFromDir(dir string, sourceDir string) (*RubyProgram, error) {
 	if _, err := os.Stat(filepath.Join(dir, "Gemfile")); err != nil {
 		return nil, fmt.Errorf("failed finding Gemfile in dir: %w", err)
 	}
-	return &RubyProgram{dir: dir, source: filepath.Join(rootDir, "harness", "ruby")}, nil
+	return &RubyProgram{dir: dir, source: sourceDir}, nil
 }
 
 // Dir is the directory to run in.