diff --git a/db/query/question_set_items.sql b/db/query/question_set_items.sql
index 4294a11..cb22474 100644
--- a/db/query/question_set_items.sql
+++ b/db/query/question_set_items.sql
@@ -4,7 +4,18 @@ INSERT INTO question_set_items (
     question_id,
     display_order
 )
-VALUES ($1, $2, COALESCE($3, 0))
+VALUES (
+    sqlc.arg('set_id'),
+    sqlc.arg('question_id'),
+    COALESCE(
+        sqlc.narg('display_order')::int,
+        COALESCE((
+            SELECT max(qsi.display_order)
+            FROM question_set_items AS qsi
+            WHERE qsi.set_id = sqlc.arg('set_id')
+        ), 0) + 1
+    )
+)
 ON CONFLICT (set_id, question_id) DO UPDATE SET display_order = EXCLUDED.display_order
 RETURNING *;
 
diff --git a/gen/db/question_set_items.sql.go b/gen/db/question_set_items.sql.go
index a9f593c..28c8ae0 100644
--- a/gen/db/question_set_items.sql.go
+++ b/gen/db/question_set_items.sql.go
@@ -17,19 +17,30 @@ INSERT INTO question_set_items (
     question_id,
     display_order
 )
-VALUES ($1, $2, COALESCE($3, 0))
+VALUES (
+    $1,
+    $2,
+    COALESCE(
+        $3::int,
+        COALESCE((
+            SELECT max(qsi.display_order)
+            FROM question_set_items AS qsi
+            WHERE qsi.set_id = $1
+        ), 0) + 1
+    )
+)
 ON CONFLICT (set_id, question_id) DO UPDATE SET display_order = EXCLUDED.display_order
 RETURNING id, set_id, question_id, display_order, created_at
 `
 
 type AddQuestionToSetParams struct {
-	SetID      int64       `json:"set_id"`
-	QuestionID int64       `json:"question_id"`
-	Column3    interface{} `json:"column_3"`
+	SetID        int64       `json:"set_id"`
+	QuestionID   int64       `json:"question_id"`
+	DisplayOrder pgtype.Int4 `json:"display_order"`
 }
 
 func (q *Queries) AddQuestionToSet(ctx context.Context, arg AddQuestionToSetParams) (QuestionSetItem, error) {
-	row := q.db.QueryRow(ctx, AddQuestionToSet, arg.SetID, arg.QuestionID, arg.Column3)
+	row := q.db.QueryRow(ctx, AddQuestionToSet, arg.SetID, arg.QuestionID, arg.DisplayOrder)
 	var i QuestionSetItem
 	err := row.Scan(
 		&i.ID,
diff --git a/internal/repository/questions.go b/internal/repository/questions.go
index 4bebecd..6090ace 100644
--- a/internal/repository/questions.go
+++ b/internal/repository/questions.go
@@ -1096,15 +1096,15 @@ func (s *Store) DeleteQuestionSet(ctx context.Context, id int64) error {
 }
 
 func (s *Store) AddQuestionToSet(ctx context.Context, setID, questionID int64, displayOrder *int32) (domain.QuestionSetItem, error) {
-	var order interface{}
+	orderParam := pgtype.Int4{Valid: false}
 	if displayOrder != nil {
-		order = *displayOrder
+		orderParam = pgtype.Int4{Int32: *displayOrder, Valid: true}
 	}
 
 	item, err := s.queries.AddQuestionToSet(ctx, dbgen.AddQuestionToSetParams{
-		SetID:      setID,
-		QuestionID: questionID,
-		Column3:    order,
+		SetID:        setID,
+		QuestionID:   questionID,
+		DisplayOrder: orderParam,
 	})
 	if err != nil {
 		return domain.QuestionSetItem{}, err
diff --git a/internal/web_server/handlers/questions.go b/internal/web_server/handlers/questions.go
index 257f280..a41cf17 100644
--- a/internal/web_server/handlers/questions.go
+++ b/internal/web_server/handlers/questions.go
@@ -58,6 +58,7 @@ type shortAnswerRes struct {
 
 type questionRes struct {
 	ID                       int64                          `json:"id"`
+	DisplayOrder             *int32                         `json:"display_order,omitempty"`
 	QuestionText             *string                        `json:"question_text,omitempty"`
 	QuestionType             string                         `json:"question_type"`
 	QuestionTypeDefinitionID *int64                         `json:"question_type_definition_id,omitempty"`
@@ -1264,8 +1265,9 @@ func (h *Handler) DeleteQuestionSet(c *fiber.Ctx) error {
 // Question Set Items
 
 type addQuestionToSetReq struct {
-	QuestionID   int64  `json:"question_id" validate:"required"`
-	DisplayOrder *int32 `json:"display_order"`
+	QuestionID int64 `json:"question_id" validate:"required"`
+	// Omit to append after the current highest display_order in the set; set explicitly to insert at a position.
+	DisplayOrder *int32 `json:"display_order,omitempty" validate:"omitempty,min=0"`
 }
 
 type questionSetItemRes struct {
@@ -1321,7 +1323,7 @@ func questionSetItemsToRes(items []domain.QuestionSetItemWithQuestion) []questio
 
 // AddQuestionToSet godoc
 // @Summary Add question to set
-// @Description Links a question to a question set
+// @Description Links a question to a question set. Omit display_order to append after the current max; the assigned value is returned in the response.
 // @Tags question-set-items
 // @Accept json
 // @Produce json
@@ -1348,6 +1350,12 @@ func (h *Handler) AddQuestionToSet(c *fiber.Ctx) error {
 			Error:   err.Error(),
 		})
 	}
+	if valErrs, ok := h.validator.Validate(c, req); !ok {
+		return c.Status(fiber.StatusBadRequest).JSON(domain.ErrorResponse{
+			Message: "Validation failed",
+			Error:   firstValidationError(valErrs),
+		})
+	}
 
 	item, err := h.questionsSvc.AddQuestionToSet(c.Context(), setID, req.QuestionID, req.DisplayOrder)
 	if err != nil {
@@ -1487,7 +1495,10 @@ func (h *Handler) GetQuestionsInSet(c *fiber.Ctx) error {
 			})
 		}
 
-		questionResponses = append(questionResponses, buildQuestionRes(question, catalog))
+		res := buildQuestionRes(question, catalog)
+		order := item.DisplayOrder
+		res.DisplayOrder = &order
+		questionResponses = append(questionResponses, res)
 	}
 
 	return c.JSON(domain.Response{