diff --git a/models/migrations/migrations.go b/models/migrations/migrations.go
index 81a618a207..be7b333a2e 100644
--- a/models/migrations/migrations.go
+++ b/models/migrations/migrations.go
@@ -415,6 +415,7 @@ func prepareMigrationTasks() []*migration {
 		newMigration(335, "Add reusable workflow fields and action_run_attempt_job_id_index table for ActionRunJob", v1_27.AddReusableWorkflowFieldsToActionRunJob),
 		newMigration(336, "Add ActionRunJobSummary table", v1_27.AddActionRunJobSummaryTable),
 		newMigration(337, "Add visibility to team", v1_27.AddVisibilityToTeam),
+		newMigration(338, "Expand legacy MSSQL issue/comment long-text columns", v1_27.ExpandIssueAndCommentLongTextFieldsForMSSQL),
 	}
 	return preparedMigrations
 }
diff --git a/models/migrations/v1_27/v338.go b/models/migrations/v1_27/v338.go
new file mode 100644
index 0000000000..a495907174
--- /dev/null
+++ b/models/migrations/v1_27/v338.go
@@ -0,0 +1,73 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package v1_27
+
+import (
+	"fmt"
+	"strings"
+
+	"gitea.dev/models/db"
+	"gitea.dev/models/migrations/base"
+
+	"xorm.io/xorm/schemas"
+)
+
+type issueWithLongTextContent struct {
+	Content string `xorm:"LONGTEXT"`
+}
+
+func (issueWithLongTextContent) TableName() string {
+	return "issue"
+}
+
+type commentWithLongTextFields struct {
+	Content     string `xorm:"LONGTEXT"`
+	PatchQuoted string `xorm:"LONGTEXT patch"`
+}
+
+func (commentWithLongTextFields) TableName() string {
+	return "comment"
+}
+
+func isMSSQLMaxTextColumn(column *schemas.Column) bool {
+	if column.Length != -1 {
+		return false
+	}
+	return strings.EqualFold(column.SQLType.Name, schemas.Varchar) || strings.EqualFold(column.SQLType.Name, schemas.NVarchar)
+}
+
+func modifyLongTextColumnsForMSSQL(x db.EngineMigration, bean any, columnNames ...string) error {
+	table, err := x.TableInfo(bean)
+	if err != nil {
+		return err
+	}
+
+	for _, columnName := range columnNames {
+		column := table.GetColumn(columnName)
+		if column == nil {
+			return fmt.Errorf("column %s does not exist in table %s", columnName, table.Name)
+		}
+		if isMSSQLMaxTextColumn(column) {
+			continue
+		}
+		if err := base.ModifyColumn(x, table.Name, column); err != nil {
+			return fmt.Errorf("modify %s.%s: %w", table.Name, columnName, err)
+		}
+	}
+
+	return nil
+}
+
+// ExpandIssueAndCommentLongTextFieldsForMSSQL expands legacy MSSQL nvarchar(4000)
+// columns to nvarchar(max) so PR push comments and long issue content are not truncated.
+func ExpandIssueAndCommentLongTextFieldsForMSSQL(x db.EngineMigration) error {
+	if x.Dialect().URI().DBType != schemas.MSSQL {
+		return nil
+	}
+
+	if err := modifyLongTextColumnsForMSSQL(x, new(issueWithLongTextContent), "content"); err != nil {
+		return err
+	}
+	return modifyLongTextColumnsForMSSQL(x, new(commentWithLongTextFields), "content", "patch")
+}
diff --git a/models/migrations/v1_27/v338_test.go b/models/migrations/v1_27/v338_test.go
new file mode 100644
index 0000000000..4e47253779
--- /dev/null
+++ b/models/migrations/v1_27/v338_test.go
@@ -0,0 +1,52 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package v1_27
+
+import (
+	"strings"
+	"testing"
+
+	"gitea.dev/models/migrations/migrationtest"
+	"gitea.dev/modules/setting"
+
+	"github.com/stretchr/testify/require"
+)
+
+type issueBeforeLongTextMSSQLMigration struct {
+	ID      int64  `xorm:"pk autoincr"`
+	Content string `xorm:"VARCHAR(4000)"`
+}
+
+func (issueBeforeLongTextMSSQLMigration) TableName() string {
+	return "issue"
+}
+
+type commentBeforeLongTextMSSQLMigration struct {
+	ID      int64  `xorm:"pk autoincr"`
+	Content string `xorm:"VARCHAR(4000)"`
+	Patch   string `xorm:"VARCHAR(4000) patch"`
+}
+
+func (commentBeforeLongTextMSSQLMigration) TableName() string {
+	return "comment"
+}
+
+func Test_ExpandIssueAndCommentLongTextFieldsForMSSQL(t *testing.T) {
+	if !setting.Database.Type.IsMSSQL() {
+		t.Skip("Only MSSQL needs to expand legacy nvarchar(4000) long-text columns")
+	}
+
+	x, deferrable := migrationtest.PrepareTestEnv(t, 0, new(issueBeforeLongTextMSSQLMigration), new(commentBeforeLongTextMSSQLMigration))
+	defer deferrable()
+
+	require.NoError(t, ExpandIssueAndCommentLongTextFieldsForMSSQL(x))
+	require.NoError(t, ExpandIssueAndCommentLongTextFieldsForMSSQL(x))
+
+	longText := strings.Repeat("x", 5000)
+	_, err := x.Insert(&issueBeforeLongTextMSSQLMigration{Content: longText})
+	require.NoError(t, err)
+
+	_, err = x.Insert(&commentBeforeLongTextMSSQLMigration{Content: longText, Patch: longText})
+	require.NoError(t, err)
+}