diff --git a/internal/db/errors.go b/internal/db/errors.go
new file mode 100644
index 0000000..7f5ad49
--- /dev/null
+++ b/internal/db/errors.go
@@ -0,0 +1,20 @@
+// Package db provides database access and migration management.
+package db
+
+import (
+	"errors"
+
+	"modernc.org/sqlite"
+	sqlite3 "modernc.org/sqlite/lib"
+)
+
+// IsUniqueConstraintError reports whether err is a SQLite
+// unique-constraint violation.
+func IsUniqueConstraintError(err error) bool {
+	var sqliteErr *sqlite.Error
+	if !errors.As(err, &sqliteErr) {
+		return false
+	}
+
+	return sqliteErr.Code() == sqlite3.SQLITE_CONSTRAINT_UNIQUE
+}
diff --git a/internal/handlers/api.go b/internal/handlers/api.go
index b1c7c87..fce5101 100644
--- a/internal/handlers/api.go
+++ b/internal/handlers/api.go
@@ -10,6 +10,7 @@ import (
 	"strings"
 	"time"
 
+	"git.eeqj.de/sneak/neoirc/internal/db"
 	"git.eeqj.de/sneak/neoirc/internal/irc"
 	"github.com/go-chi/chi"
 )
@@ -199,7 +200,7 @@ func (hdlr *Handlers) handleCreateSessionError(
 	request *http.Request,
 	err error,
 ) {
-	if strings.Contains(err.Error(), "UNIQUE") {
+	if db.IsUniqueConstraintError(err) {
 		hdlr.respondError(
 			writer, request,
 			"nick already taken",
@@ -1427,7 +1428,7 @@ func (hdlr *Handlers) executeNickChange(
 		request.Context(), sessionID, newNick,
 	)
 	if err != nil {
-		if strings.Contains(err.Error(), "UNIQUE") {
+		if db.IsUniqueConstraintError(err) {
 			hdlr.respondIRCError(
 				writer, request, clientID, sessionID,
 				irc.ErrNicknameInUse, nick, []string{newNick},
diff --git a/internal/handlers/auth.go b/internal/handlers/auth.go
index ceb320f..cd99bf7 100644
--- a/internal/handlers/auth.go
+++ b/internal/handlers/auth.go
@@ -4,6 +4,8 @@ import (
 	"encoding/json"
 	"net/http"
 	"strings"
+
+	"git.eeqj.de/sneak/neoirc/internal/db"
 )
 
 const minPasswordLength = 8
@@ -94,7 +96,7 @@ func (hdlr *Handlers) handleRegisterError(
 	request *http.Request,
 	err error,
 ) {
-	if strings.Contains(err.Error(), "UNIQUE") {
+	if db.IsUniqueConstraintError(err) {
 		hdlr.respondError(
 			writer, request,
 			"nick already taken",