diff --git a/migrator/migrator.go b/migrator/migrator.go
index af1385e2..91bf60a7 100644
--- a/migrator/migrator.go
+++ b/migrator/migrator.go
@@ -390,7 +390,7 @@ func (m Migrator) MigrateColumn(value interface{}, field *schema.Field, columnTy
 	alterColumn := false
 
 	// check size
-	if length, _ := columnType.Length(); length != int64(field.Size) {
+	if length, ok := columnType.Length(); length != int64(field.Size) {
 		if length > 0 && field.Size > 0 {
 			alterColumn = true
 		} else {
@@ -399,7 +399,7 @@ func (m Migrator) MigrateColumn(value interface{}, field *schema.Field, columnTy
 			matches := regRealDataType.FindAllStringSubmatch(realDataType, -1)
 			matches2 := regFullDataType.FindAllStringSubmatch(fullDataType, -1)
 			if (len(matches) == 1 && matches[0][1] != fmt.Sprint(field.Size) || !field.PrimaryKey) &&
-				(len(matches2) == 1 && matches2[0][1] != fmt.Sprint(length)) {
+				(len(matches2) == 1 && matches2[0][1] != fmt.Sprint(length) && ok) {
 				alterColumn = true
 			}
 		}
diff --git a/tests/migrate_test.go b/tests/migrate_test.go
index 789a5e45..3d15bf2c 100644
--- a/tests/migrate_test.go
+++ b/tests/migrate_test.go
@@ -90,7 +90,7 @@ func TestAutoMigrateSelfReferential(t *testing.T) {
 }
 
 func TestSmartMigrateColumn(t *testing.T) {
-	fullSupported := map[string]bool{"mysql": true, "postgres": true}[DB.Dialector.Name()]
+	fullSupported := map[string]bool{"mysql": true}[DB.Dialector.Name()]
 
 	type UserMigrateColumn struct {
 		ID       uint