diff --git a/migrator/migrator.go b/migrator/migrator.go
index 29c0c00c..9f8e3db8 100644
--- a/migrator/migrator.go
+++ b/migrator/migrator.go
@@ -406,17 +406,14 @@ func (m Migrator) MigrateColumn(value interface{}, field *schema.Field, columnTy
 	fullDataType := strings.TrimSpace(strings.ToLower(m.DB.Migrator().FullDataTypeOf(field).SQL))
 	realDataType := strings.ToLower(columnType.DatabaseTypeName())
 
-	alterColumn := false
+	var (
+		alterColumn, isSameType bool
+	)
 
 	if !field.PrimaryKey {
 		// check type
-		var isSameType bool
-		if strings.HasPrefix(fullDataType, realDataType) {
-			isSameType = true
-		}
-
-		// check type aliases
-		if !isSameType {
+		if !strings.HasPrefix(fullDataType, realDataType) {
+			// check type aliases
 			aliases := m.DB.Migrator().GetTypeAliases(realDataType)
 			for _, alias := range aliases {
 				if strings.HasPrefix(fullDataType, alias) {
@@ -424,32 +421,34 @@ func (m Migrator) MigrateColumn(value interface{}, field *schema.Field, columnTy
 					break
 				}
 			}
-		}
 
-		if !isSameType {
-			alterColumn = true
-		}
-	}
-
-	// check size
-	if length, ok := columnType.Length(); length != int64(field.Size) {
-		if length > 0 && field.Size > 0 {
-			alterColumn = true
-		} else {
-			// has size in data type and not equal
-			// Since the following code is frequently called in the for loop, reg optimization is needed here
-			matches2 := regFullDataType.FindAllStringSubmatch(fullDataType, -1)
-			if !field.PrimaryKey &&
-				(len(matches2) == 1 && matches2[0][1] != fmt.Sprint(length) && ok) {
+			if !isSameType {
 				alterColumn = true
 			}
 		}
 	}
 
-	// check precision
-	if precision, _, ok := columnType.DecimalSize(); ok && int64(field.Precision) != precision {
-		if regexp.MustCompile(fmt.Sprintf("[^0-9]%d[^0-9]", field.Precision)).MatchString(m.DataTypeOf(field)) {
-			alterColumn = true
+	if !isSameType {
+		// check size
+		if length, ok := columnType.Length(); length != int64(field.Size) {
+			if length > 0 && field.Size > 0 {
+				alterColumn = true
+			} else {
+				// has size in data type and not equal
+				// Since the following code is frequently called in the for loop, reg optimization is needed here
+				matches2 := regFullDataType.FindAllStringSubmatch(fullDataType, -1)
+				if !field.PrimaryKey &&
+					(len(matches2) == 1 && matches2[0][1] != fmt.Sprint(length) && ok) {
+					alterColumn = true
+				}
+			}
+		}
+
+		// check precision
+		if precision, _, ok := columnType.DecimalSize(); ok && int64(field.Precision) != precision {
+			if regexp.MustCompile(fmt.Sprintf("[^0-9]%d[^0-9]", field.Precision)).MatchString(m.DataTypeOf(field)) {
+				alterColumn = true
+			}
 		}
 	}
 
diff --git a/tests/migrate_test.go b/tests/migrate_test.go
index b918b4b5..8718aa57 100644
--- a/tests/migrate_test.go
+++ b/tests/migrate_test.go
@@ -1,6 +1,7 @@
 package tests_test
 
 import (
+	"context"
 	"fmt"
 	"math/rand"
 	"reflect"
@@ -9,6 +10,7 @@ import (
 	"time"
 
 	"gorm.io/driver/postgres"
+
 	"gorm.io/gorm"
 	"gorm.io/gorm/schema"
 	. "gorm.io/gorm/utils/tests"
@@ -72,6 +74,44 @@ func TestMigrate(t *testing.T) {
 			t.Fatalf("Failed to find index for many2many for %v %v", indexes[0], indexes[1])
 		}
 	}
+
+}
+
+func TestAutoMigrateInt8PG(t *testing.T) {
+	if DB.Dialector.Name() != "postgres" {
+		return
+	}
+
+	type Smallint int8
+
+	type MigrateInt struct {
+		Int8 Smallint
+	}
+
+	tracer := Tracer{
+		Logger: DB.Config.Logger,
+		Test: func(ctx context.Context, begin time.Time, fc func() (sql string, rowsAffected int64), err error) {
+			sql, _ := fc()
+			if strings.HasPrefix(sql, "ALTER TABLE \"migrate_ints\" ALTER COLUMN \"int8\" TYPE smallint") {
+				t.Fatalf("shouldn't execute ALTER COLUMN TYPE if such type is already existed in DB schema: sql: %s", sql)
+			}
+		},
+	}
+
+	DB.Migrator().DropTable(&MigrateInt{})
+
+	// The first AutoMigrate to make table with field with correct type
+	if err := DB.AutoMigrate(&MigrateInt{}); err != nil {
+		t.Fatalf("Failed to auto migrate: error: %v", err)
+	}
+
+	// make new session to set custom logger tracer
+	session := DB.Session(&gorm.Session{Logger: tracer})
+
+	// The second AutoMigrate to catch an error
+	if err := session.AutoMigrate(&MigrateInt{}); err != nil {
+		t.Fatalf("Failed to auto migrate: error: %v", err)
+	}
 }
 
 func TestAutoMigrateSelfReferential(t *testing.T) {
diff --git a/tests/tracer_test.go b/tests/tracer_test.go
new file mode 100644
index 00000000..3e9a4052
--- /dev/null
+++ b/tests/tracer_test.go
@@ -0,0 +1,34 @@
+package tests_test
+
+import (
+	"context"
+	"time"
+
+	"gorm.io/gorm/logger"
+)
+
+type Tracer struct {
+	Logger logger.Interface
+	Test   func(ctx context.Context, begin time.Time, fc func() (sql string, rowsAffected int64), err error)
+}
+
+func (S Tracer) LogMode(level logger.LogLevel) logger.Interface {
+	return S.Logger.LogMode(level)
+}
+
+func (S Tracer) Info(ctx context.Context, s string, i ...interface{}) {
+	S.Logger.Info(ctx, s, i...)
+}
+
+func (S Tracer) Warn(ctx context.Context, s string, i ...interface{}) {
+	S.Logger.Warn(ctx, s, i...)
+}
+
+func (S Tracer) Error(ctx context.Context, s string, i ...interface{}) {
+	S.Logger.Error(ctx, s, i...)
+}
+
+func (S Tracer) Trace(ctx context.Context, begin time.Time, fc func() (sql string, rowsAffected int64), err error) {
+	S.Logger.Trace(ctx, begin, fc, err)
+	S.Test(ctx, begin, fc, err)
+}