diff --git a/Cicm.Database/Models/InstructionSetExtension.cs b/Cicm.Database/Models/InstructionSetExtension.cs
index d3c09046..40309da9 100644
--- a/Cicm.Database/Models/InstructionSetExtension.cs
+++ b/Cicm.Database/Models/InstructionSetExtension.cs
@@ -31,6 +31,7 @@
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.ComponentModel.DataAnnotations;
+using Microsoft.AspNetCore.Mvc;
 
 namespace Cicm.Database.Models
 {
@@ -44,6 +45,7 @@ namespace Cicm.Database.Models
         [DisplayName("Name")]
         [Required]
         [StringLength(45)]
+        [Remote("VerifyUnique", "InstructionSetExtensions", "Admin")]
         public string Extension { get; set; }
 
         public virtual ICollection<InstructionSetExtensionsByProcessor> InstructionSetExtensionsByProcessor
diff --git a/cicm_web/Areas/Admin/Controllers/InstructionSetExtensionsController.cs b/cicm_web/Areas/Admin/Controllers/InstructionSetExtensionsController.cs
index e7b62bd2..f5c90015 100644
--- a/cicm_web/Areas/Admin/Controllers/InstructionSetExtensionsController.cs
+++ b/cicm_web/Areas/Admin/Controllers/InstructionSetExtensionsController.cs
@@ -28,6 +28,7 @@
 // Copyright © 2003-2018 Natalia Portillo
 *******************************************************************************/
 
+using System;
 using System.Linq;
 using System.Threading.Tasks;
 using Cicm.Database.Models;
@@ -49,7 +50,8 @@ namespace cicm_web.Areas.Admin.Controllers
         }
 
         // GET: Admin/InstructionSetExtensions
-        public async Task<IActionResult> Index() => View(await _context.InstructionSetExtensions.OrderBy(e => e.Extension).ToListAsync());
+        public async Task<IActionResult> Index() =>
+            View(await _context.InstructionSetExtensions.OrderBy(e => e.Extension).ToListAsync());
 
         // GET: Admin/InstructionSetExtensions/Details/5
         public async Task<IActionResult> Details(int? id)
@@ -152,5 +154,12 @@ namespace cicm_web.Areas.Admin.Controllers
         {
             return _context.InstructionSetExtensions.Any(e => e.Id == id);
         }
+
+        [AcceptVerbs("Get", "Post")]
+        public IActionResult VerifyUnique(string extension) =>
+            _context.InstructionSetExtensions.Any(i => string.Equals(i.Extension, extension,
+                                                                     StringComparison.InvariantCultureIgnoreCase))
+                ? Json("Instruction set extension already exists.")
+                : Json(true);
     }
 }
\ No newline at end of file
diff --git a/cicm_web/cicm_web.csproj b/cicm_web/cicm_web.csproj
index 99f3dd9d..14df1dda 100644
--- a/cicm_web/cicm_web.csproj
+++ b/cicm_web/cicm_web.csproj
@@ -2,7 +2,7 @@
 <Project Sdk="Microsoft.NET.Sdk.Web">
   <PropertyGroup>
     <TargetFramework>netcoreapp2.2</TargetFramework>
-    <Version>3.0.99.520</Version>
+    <Version>3.0.99.521</Version>
     <Company>Canary Islands Computer Museum</Company>
     <Copyright>Copyright © 2003-2018 Natalia Portillo</Copyright>
     <Product>Canary Islands Computer Museum Website</Product>