diff --git a/internal/db/db.go b/internal/db/db.go
index 824ae05..e133fc0 100644
--- a/internal/db/db.go
+++ b/internal/db/db.go
@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"regexp"
 	"sync"
+	"uuid"
 
 	"github.com/mattn/go-sqlite3"
 )
@@ -55,6 +56,13 @@ func Connect(ctx context.Context, cfg Config) (*SQLite, error) {
 	driverOnce.Do(func() {
 		sql.Register("odidere_sqlite", &sqlite3.SQLiteDriver{
 			ConnectHook: func(conn *sqlite3.SQLiteConn) error {
+				if err := conn.RegisterFunc(
+					"uuid4",
+					func() string { return uuid.New().String() },
+					false,
+				); err != nil {
+					return fmt.Errorf("failed to register uuid4: %w", err)
+				}
 				if err := conn.RegisterFunc(
 					"regexp",
 					func(re, s string) (bool, error) {
diff --git a/internal/db/queries.go b/internal/db/queries.go
index 9dc22a0..acdd1f8 100644
--- a/internal/db/queries.go
+++ b/internal/db/queries.go
@@ -313,6 +313,8 @@ type InsertMessageParams struct {
 	Content string
 	// ConversationId identifies the conversation that owns the new row.
 	ConversationId string
+	// Id is the new row's UUID. Nil generates a version 4 UUID.
+	Id *uuid.UUID
 	// Metadata is inference JSON converted to JSONB for storage.
 	// Nil stores SQL NULL; malformed JSON causes insertion to fail.
 	Metadata jsontext.Value
@@ -324,6 +326,12 @@ type InsertMessageParams struct {
 
 // InsertMessage creates a new message.
 func (q *Queries) InsertMessage(ctx context.Context, arg InsertMessageParams) (*Message, error) {
+	var id uuid.UUID
+	if arg.Id == nil {
+		id = uuid.NewV4()
+	} else {
+		id = *arg.Id
+	}
 	var metadataArg any
 	if arg.Metadata != nil {
 		metadataArg = string(arg.Metadata)
@@ -331,7 +339,7 @@ func (q *Queries) InsertMessage(ctx context.Context, arg InsertMessageParams) (*
 	row := q.db.QueryRowContext(
 		ctx,
 		insertMessage,
-		uuid.New().String(),
+		id.String(),
 		arg.Content,
 		arg.ConversationId,
 		metadataArg,
diff --git a/internal/db/queries_test.go b/internal/db/queries_test.go
index 7e3bb03..279a3ae 100644
--- a/internal/db/queries_test.go
+++ b/internal/db/queries_test.go
@@ -8,6 +8,7 @@ import (
 	"log/slog"
 	"reflect"
 	"testing"
+	"uuid"
 
 	"github.com/mattn/go-sqlite3"
 )
@@ -344,6 +345,53 @@ func testMessaging(t *testing.T, ctx context.Context, db *SQLite) {
 			}
 		})
 	}
+	suppliedID := uuid.NewV4()
+	for _, tt := range []struct {
+		name    string
+		id      *uuid.UUID
+		wantErr bool
+	}{
+		{name: "generated ID"},
+		{name: "supplied v4 ID", id: &suppliedID},
+		{name: "duplicate ID", id: &suppliedID, wantErr: true},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			seq, err := qw.NextSequence(ctx, c.Id)
+			if err != nil {
+				t.Fatal(err)
+			}
+			inserted, err := qw.InsertMessage(ctx, InsertMessageParams{
+				Content:        `{"role":"assistant","content":"answer"}`,
+				ConversationId: c.Id,
+				Id:             tt.id,
+				Role:           MessageRoleAssistant,
+				Sequence:       seq,
+			})
+			if tt.wantErr {
+				if err == nil {
+					t.Fatal("duplicate ID was accepted")
+				}
+				return
+			}
+			if err != nil {
+				t.Fatal(err)
+			}
+			if _, err := uuid.Parse(inserted.Id); err != nil {
+				t.Fatal(err)
+			}
+			if tt.id != nil && inserted.Id != tt.id.String() {
+				t.Errorf("inserted ID = %s, want %s", inserted.Id, tt.id.String())
+			}
+			if tt.id == nil {
+				if err := qw.DeleteMessageId(ctx, inserted.Id); err != nil {
+					t.Fatal(err)
+				}
+			}
+		})
+	}
+	if err := qw.DeleteMessageId(ctx, suppliedID.String()); err != nil {
+		t.Fatal(err)
+	}
 	tx, err := db.Writer.BeginTx(ctx, nil)
 	if err != nil {
 		t.Fatal(err)