diff --git a/entc/gen/type.go b/entc/gen/type.go
index ac70a21277..2ac5461abd 100644
--- a/entc/gen/type.go
+++ b/entc/gen/type.go
@@ -239,6 +239,9 @@ 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 cannot be optional")
+			}
 			typ.ID = tf
 		} else {
 			typ.Fields = append(typ.Fields, tf)
diff --git a/entc/gen/type_test.go b/entc/gen/type_test.go
index d70c31314c..89a04ac104 100644
--- a/entc/gen/type_test.go
+++ b/entc/gen/type_test.go
@@ -25,17 +25,17 @@ func TestType(t *testing.T) {
 
 	_, err = NewType(&Config{Package: "entc/gen"}, &load.Schema{
 		Fields: []*load.Field{
-			{Unique: true, Default: true, Info: &field.TypeInfo{Type: field.TypeInt}},
+			{Name: "foo", Unique: true, Default: true, Info: &field.TypeInfo{Type: field.TypeInt}},
 		},
 	})
-	require.Error(err, "unique field can not have default")
+	require.EqualError(err, "unique field \"foo\" cannot have default value", "unique field can not have default")
 
 	_, err = NewType(&Config{Package: "entc/gen"}, &load.Schema{
 		Fields: []*load.Field{
-			{Sensitive: true, Tag: `yaml:"pwd"`, Info: &field.TypeInfo{Type: field.TypeString}},
+			{Name: "foo", Sensitive: true, Tag: `yaml:"pwd"`, Info: &field.TypeInfo{Type: field.TypeString}},
 		},
 	})
-	require.Error(err, "sensitive field cannot have tags")
+	require.EqualError(err, "sensitive field \"foo\" cannot have struct tags", "sensitive field cannot have tags")
 
 	_, err = NewType(&Config{Package: "entc/gen"}, &load.Schema{
 		Name: "T",
@@ -44,7 +44,7 @@ func TestType(t *testing.T) {
 			{Name: "foo", Unique: true, Info: &field.TypeInfo{Type: field.TypeInt}},
 		},
 	})
-	require.Error(err, "field foo redeclared")
+	require.EqualError(err, "field \"foo\" redeclared for type \"T\"", "field foo redeclared")
 
 	_, err = NewType(&Config{Package: "entc/gen"}, &load.Schema{
 		Name: "T",
@@ -52,7 +52,7 @@ func TestType(t *testing.T) {
 			{Name: "enums", Info: &field.TypeInfo{Type: field.TypeEnum}, Enums: []struct{ N, V string }{{V: "v"}, {V: "v"}}},
 		},
 	})
-	require.Error(err, "duplicate enums")
+	require.EqualError(err, "duplicate values \"v\" for enum field \"enums\"", "duplicate enums")
 
 	_, err = NewType(&Config{Package: "entc/gen"}, &load.Schema{
 		Name: "T",
@@ -60,7 +60,7 @@ func TestType(t *testing.T) {
 			{Name: "enums", Info: &field.TypeInfo{Type: field.TypeEnum}, Enums: []struct{ N, V string }{{}}},
 		},
 	})
-	require.Error(err, "empty value for enums")
+	require.EqualError(err, "\"enums\" field value cannot be empty", "empty value for enums")
 
 	_, err = NewType(&Config{Package: "entc/gen"}, &load.Schema{
 		Name: "T",
@@ -68,7 +68,15 @@ func TestType(t *testing.T) {
 			{Name: "", Info: &field.TypeInfo{Type: field.TypeInt}},
 		},
 	})
-	require.Error(err, "empty field name")
+	require.EqualError(err, "field name cannot be empty", "empty field name")
+
+	_, err = NewType(&Config{Package: "entc/gen"}, &load.Schema{
+		Name: "T",
+		Fields: []*load.Field{
+			{Name: "id", Info: &field.TypeInfo{Type: field.TypeInt}, Optional: true},
+		},
+	})
+	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\"")