diff --git a/internal/git/service.go b/internal/git/service.go
index 8163633..6acf1a9 100644
--- a/internal/git/service.go
+++ b/internal/git/service.go
@@ -7,12 +7,19 @@ import (
 	"strings"
 )
 
-type Service struct{}
+type Service struct{
+	diffTarget string
+}
 
 func NewService() *Service {
 	return &Service{}
 }
 
+// SetDiffTarget sets the target for git diff (e.g., "main", "HEAD~1", commit hash)
+func (s *Service) SetDiffTarget(target string) {
+	s.diffTarget = target
+}
+
 // GetDiff retrieves the git diff with optional context lines (default: 3)
 func (s *Service) GetDiff(diffType DiffType, contextLines ...int) (*DiffResult, error) {
 	context := 3
@@ -22,13 +29,18 @@ func (s *Service) GetDiff(diffType DiffType, contextLines ...int) (*DiffResult,
 
 	var args []string
 
-	switch diffType {
-	case DiffTypeStaged:
-		args = []string{"diff", "--cached", "--no-color", "--no-ext-diff"}
-	case DiffTypeUnstaged:
-		args = []string{"diff", "--no-color", "--no-ext-diff"}
-	default:
-		args = []string{"diff", "HEAD", "--no-color", "--no-ext-diff"}
+	// If a diff target is specified, use it instead of the default behavior
+	if s.diffTarget != "" {
+		args = []string{"diff", s.diffTarget, "--no-color", "--no-ext-diff"}
+	} else {
+		switch diffType {
+		case DiffTypeStaged:
+			args = []string{"diff", "--cached", "--no-color", "--no-ext-diff"}
+		case DiffTypeUnstaged:
+			args = []string{"diff", "--no-color", "--no-ext-diff"}
+		default:
+			args = []string{"diff", "HEAD", "--no-color", "--no-ext-diff"}
+		}
 	}
 
 	// Add context parameter
diff --git a/main.go b/main.go
index 16806ed..edea5d4 100644
--- a/main.go
+++ b/main.go
@@ -86,9 +86,16 @@ func main() {
 		os.Setenv("VIBEDIFF_DEBUG", "true")
 	}
 
+	// Get diff target from positional argument
+	var target string
+	if flag.NArg() > 0 {
+		target = flag.Arg(0)
+	}
+
 	reviewStore := review.NewStore()
 
 	gitService := git.NewService()
+	gitService.SetDiffTarget(target)
 	handler := handlers.NewHandler(gitService, reviewStore)
 	handler.SetFormat(*format)