diff --git a/service/service.go b/service/service.go
index 95d2fee..c048482 100644
--- a/service/service.go
+++ b/service/service.go
@@ -39,27 +39,30 @@ func New(s store.Store, opts Options) (*Service, error) {
 		return nil, errors.New("pase: store is required")
 	}
 
-	if opts.IDGenerator == nil {
-		opts.IDGenerator = DefaultIDGenerator()
+	idGenerator := DefaultIDGenerator()
+	if opts.IDGenerator != nil {
+		idGenerator = opts.IDGenerator
 	}
 
+	operationTimeout := DefaultOperationTimeout
 	if opts.OperationTimeout < 0 {
 		return nil, errors.New("pase: OperationTimeout must be non-negative")
-	} else if opts.OperationTimeout == 0 {
-		opts.OperationTimeout = DefaultOperationTimeout
+	} else if opts.OperationTimeout != 0 {
+		operationTimeout = opts.OperationTimeout
 	}
 
+	magicLinkTTL := DefaultMagicLinkTTL
 	if opts.MagicLinkTTL < 0 {
 		return nil, errors.New("pase: MagicLinkTTL must be non-negative")
-	} else if opts.MagicLinkTTL == 0 {
-		opts.MagicLinkTTL = DefaultMagicLinkTTL
+	} else if opts.MagicLinkTTL != 0 {
+		magicLinkTTL = opts.MagicLinkTTL
 	}
 
 	return &Service{
 		store:            s,
-		idGenerator:      opts.IDGenerator,
-		operationTimeout: opts.OperationTimeout,
-		magicLinkTTL:     opts.MagicLinkTTL,
+		idGenerator:      idGenerator,
+		operationTimeout: operationTimeout,
+		magicLinkTTL:     magicLinkTTL,
 	}, nil
 }