diff --git a/types/commit.go b/types/commit.go
index e25f0a3a..6dccc235 100644
--- a/types/commit.go
+++ b/types/commit.go
@@ -149,7 +149,7 @@ func (c *Commit) Payload() string {
 		for _, p := range c.ParentHashes {
 			fmt.Fprintf(&payload, "parent %s\n", p.String())
 		}
-	} else {
+	} else if c.Parent != "" {
 		// present for backwards compatibility
 		fmt.Fprintf(&payload, "parent %s\n", c.Parent)
 	}
diff --git a/types/commit_test.go b/types/commit_test.go
new file mode 100644
index 00000000..ef52c779
--- /dev/null
+++ b/types/commit_test.go
@@ -0,0 +1,69 @@
+package types
+
+import (
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/go-git/go-git/v5/plumbing"
+	"github.com/go-git/go-git/v5/plumbing/object"
+)
+
+func TestPayloadRootCommit(t *testing.T) {
+	when := time.Date(2025, 1, 1, 12, 0, 0, 0, time.UTC)
+	sig := object.Signature{Name: "Alice", Email: "alice@example.com", When: when}
+
+	c := Commit{
+		Author:    sig,
+		Committer: sig,
+		Message:   "initial commit\n",
+		Tree:      "abc123",
+	}
+
+	payload := c.Payload()
+
+	for _, line := range strings.Split(payload, "\n") {
+		if strings.HasPrefix(line, "parent ") || line == "parent" {
+			t.Errorf("root commit payload must not contain a parent line, got: %q\nfull payload:\n%s", line, payload)
+		}
+	}
+}
+
+func TestPayloadWithParentHashes(t *testing.T) {
+	when := time.Date(2025, 1, 1, 12, 0, 0, 0, time.UTC)
+	sig := object.Signature{Name: "Alice", Email: "alice@example.com", When: when}
+	parent := plumbing.NewHash("0000000000000000000000000000000000000001")
+
+	c := Commit{
+		Author:       sig,
+		Committer:    sig,
+		Message:      "second commit\n",
+		Tree:         "abc123",
+		ParentHashes: []plumbing.Hash{parent},
+	}
+
+	payload := c.Payload()
+	want := "parent " + parent.String()
+	if !strings.Contains(payload, want) {
+		t.Errorf("payload missing %q\nfull payload:\n%s", want, payload)
+	}
+}
+
+func TestPayloadLegacyParentField(t *testing.T) {
+	when := time.Date(2025, 1, 1, 12, 0, 0, 0, time.UTC)
+	sig := object.Signature{Name: "Alice", Email: "alice@example.com", When: when}
+
+	c := Commit{
+		Author:    sig,
+		Committer: sig,
+		Message:   "second commit\n",
+		Tree:      "abc123",
+		Parent:    "0000000000000000000000000000000000000001",
+	}
+
+	payload := c.Payload()
+	want := "parent 0000000000000000000000000000000000000001"
+	if !strings.Contains(payload, want) {
+		t.Errorf("payload missing %q\nfull payload:\n%s", want, payload)
+	}
+}