diff --git a/modules/lagoon/README.md b/modules/lagoon/README.md
index 7be2b71..64bf28c 100644
--- a/modules/lagoon/README.md
+++ b/modules/lagoon/README.md
@@ -15,7 +15,7 @@ Postgres data layer: the shared GORM connection, per-plugin migrations, model he
 - One shared pool: `lagoon.Open`, `lagoon.Use` and `lagoon.OpenFromApp` return a `*sql.DB` and a `*gorm.DB` built on that same pool; `lagoon.Publish` makes both available on the `backpack.App`.
 - Database check at connect time: `lagoon.CheckLocale` refuses a database whose default collation is not the ICU `pl-PL` locale, so ordering matches the database default without per-query `COLLATE`.
 - Per-plugin migrations: `lagoon.Migrate` runs the framework's `system_files` set (`attach.Migrations`) and backend admin identity set (`lagoon.BackendAdminMigrations`), then every `pact.HasMigrations` set in plugin activation order, each in its own `summer_migrations_<plugin_id>` history table (`lagoon.HistoryTableName`). `lagoon.RollbackLast` and `lagoon.Status` cover rollback and history.
-- Mass assignment: `lagoon.Fill` copies only allow-listed keys onto a model by GORM column name and silently drops the rest, logging each dropped key once outside production. `lagoon.HasFillable` and `lagoon.HasHidden` are the Go forms of `$fillable` and `$hidden`.
+- Mass assignment: `lagoon.Fill` copies only allow-listed keys onto a model by GORM column name and silently drops the rest, logging each dropped key once outside production. A `json.Number` (from a decoder using `UseNumber`) fills integer, unsigned and float fields, and a fraction or an overflow is an error. `lagoon.HasFillable` and `lagoon.HasHidden` are the Go forms of `$fillable` and `$hidden`.
 - Validation: `lagoon.Validate` accepts Laravel-style rule strings (`required`, `nullable`, `integer`, `numeric`, `between`, `min`, `max`, `in`, `unique`, `boolean`, `email`, `confirmed`, `different`, `mimes`) and returns a field-to-messages map, translated through phrasebook when a translator is given. Unknown rule tokens are an error.
 - Safe ordering: `lagoon.OrderBy` appends an ORDER BY only for an allow-listed column and an `asc` or `desc` direction.
 - Pagination: `lagoon.Paginate` builds a `lagoon.Page` with `data` and `meta` (`current_page`, `last_page`, `per_page`, `total`).
diff --git a/modules/lagoon/fill.go b/modules/lagoon/fill.go
index 5cdfa83..bf403e2 100644
--- a/modules/lagoon/fill.go
+++ b/modules/lagoon/fill.go
@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"log/slog"
 	"reflect"
+	"strconv"
 	"strings"
 	"sync"
 )
@@ -159,12 +160,49 @@ func convertValue(src reflect.Value, destType reflect.Type) (reflect.Value, erro
 	if src.Type().AssignableTo(destType) {
 		return src, nil
 	}
+	if n, ok := src.Interface().(json.Number); ok {
+		if out, handled, err := convertNumber(n, destType); handled {
+			return out, err
+		}
+	}
 	if src.Type().ConvertibleTo(destType) {
 		return src.Convert(destType), nil
 	}
 	return reflect.Value{}, fmt.Errorf("cannot assign %s to %s", src.Type(), destType)
 }
 
+// convertNumber parses a json.Number, which a request decoder using
+// UseNumber produces, into an integer, unsigned or float field. A value that
+// does not parse as that kind or overflows it is an error. handled is false
+// for any other destination kind, so a string field still takes the number's
+// text through the ordinary conversion.
+func convertNumber(n json.Number, destType reflect.Type) (reflect.Value, bool, error) {
+	out := reflect.New(destType).Elem()
+	switch destType.Kind() {
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		i, err := strconv.ParseInt(n.String(), 10, 64)
+		if err != nil || out.OverflowInt(i) {
+			return reflect.Value{}, true, fmt.Errorf("cannot assign number %s to %s", n, destType)
+		}
+		out.SetInt(i)
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+		u, err := strconv.ParseUint(n.String(), 10, 64)
+		if err != nil || out.OverflowUint(u) {
+			return reflect.Value{}, true, fmt.Errorf("cannot assign number %s to %s", n, destType)
+		}
+		out.SetUint(u)
+	case reflect.Float32, reflect.Float64:
+		f, err := strconv.ParseFloat(n.String(), 64)
+		if err != nil || out.OverflowFloat(f) {
+			return reflect.Value{}, true, fmt.Errorf("cannot assign number %s to %s", n, destType)
+		}
+		out.SetFloat(f)
+	default:
+		return reflect.Value{}, false, nil
+	}
+	return out, true, nil
+}
+
 // encryptedFromRequest treats request input for an Encrypted column as
 // plaintext. It never falls through to Encrypted.Scan: Scan decrypts, so a
 // write path that scanned request input would reject real secrets and accept
diff --git a/modules/lagoon/fill_test.go b/modules/lagoon/fill_test.go
index 649c281..bf689a5 100644
--- a/modules/lagoon/fill_test.go
+++ b/modules/lagoon/fill_test.go
@@ -2,6 +2,7 @@ package lagoon
 
 import (
 	"bytes"
+	"encoding/json"
 	"log/slog"
 	"strings"
 	"testing"
@@ -160,3 +161,35 @@ func TestFillEncryptedTakesPlaintext(t *testing.T) {
 		t.Fatalf("nil must clear: api_key=%q token=%v", row.APIKey.Reveal(), row.Token)
 	}
 }
+
+// TestFillJSONNumber covers request bodies decoded with UseNumber: a
+// json.Number fills integer, unsigned and float fields (plain or pointer), a
+// string field keeps the number's text, and a fraction or an overflow into an
+// integer field is an error rather than a silent truncation.
+func TestFillJSONNumber(t *testing.T) {
+	type numbers struct {
+		Year  *int    `gorm:"column:year"`
+		Count uint8   `gorm:"column:count"`
+		Price float64 `gorm:"column:price"`
+		Code  string  `gorm:"column:code"`
+	}
+	allowed := []string{"year", "count", "price", "code"}
+	var row numbers
+	err := Fill(&row, allowed, map[string]any{
+		"year":  json.Number("1977"),
+		"count": json.Number("200"),
+		"price": json.Number("12.5"),
+		"code":  json.Number("0042"),
+	}, true)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if row.Year == nil || *row.Year != 1977 || row.Count != 200 || row.Price != 12.5 || row.Code != "0042" {
+		t.Fatalf("row = %+v (year %v)", row, row.Year)
+	}
+	for key, value := range map[string]json.Number{"year": "1977.5", "count": "256"} {
+		if err := Fill(&row, allowed, map[string]any{key: value}, true); err == nil {
+			t.Fatalf("%s = %s filled without an error", key, value)
+		}
+	}
+}