diff --git a/entc/gen/type.go b/entc/gen/type.go
index 1f2b521bf7..2ac5461abd 100644
--- a/entc/gen/type.go
+++ b/entc/gen/type.go
@@ -240,7 +240,7 @@ func NewType(c *Config, schema *load.Schema) (*Type, error) {
 		// User defined id field.
 		if tf.Name == typ.ID.Name {
 			if tf.Optional {
-				return nil, fmt.Errorf("id field must not be optional")
+				return nil, fmt.Errorf("id field cannot be optional")
 			}
 			typ.ID = tf
 		} else {
diff --git a/entc/gen/type_test.go b/entc/gen/type_test.go
index 032f9fad76..89a04ac104 100644
--- a/entc/gen/type_test.go
+++ b/entc/gen/type_test.go
@@ -76,7 +76,7 @@ func TestType(t *testing.T) {
 			{Name: "id", Info: &field.TypeInfo{Type: field.TypeInt}, Optional: true},
 		},
 	})
-	require.EqualError(err, "id field must not be optional", "id field can't be optional")
+	require.EqualError(err, "id field cannot be optional", "id field cannot be optional")
 
 	_, err = NewType(&Config{Package: "entc/gen"}, &load.Schema{Name: "Type"})
 	require.EqualError(err, "schema lowercase name conflicts with Go keyword \"type\"")