diff --git a/Cicm.Database/Models/InstructionSetExtensionsByProcessor.cs b/Cicm.Database/Models/InstructionSetExtensionsByProcessor.cs
index 3089253e..0425aefb 100644
--- a/Cicm.Database/Models/InstructionSetExtensionsByProcessor.cs
+++ b/Cicm.Database/Models/InstructionSetExtensionsByProcessor.cs
@@ -28,11 +28,15 @@
 // Copyright © 2003-2018 Natalia Portillo
 *******************************************************************************/
 
+using Microsoft.AspNetCore.Mvc;
+
 namespace Cicm.Database.Models
 {
     public class InstructionSetExtensionsByProcessor : BaseModel<int>
     {
+        [Remote("VerifyUnique", "InstructionSetExtensionsByProcessor", "Admin", AdditionalFields = nameof(ExtensionId))]
         public int ProcessorId { get; set; }
+        [Remote("VerifyUnique", "InstructionSetExtensionsByProcessor", "Admin", AdditionalFields = nameof(ProcessorId))]
         public int ExtensionId { get; set; }
 
         public virtual InstructionSetExtension Extension { get; set; }
diff --git a/cicm_web/Areas/Admin/Controllers/InstructionSetExtensionsByProcessorController.cs b/cicm_web/Areas/Admin/Controllers/InstructionSetExtensionsByProcessorController.cs
index c6e5c767..9815ff96 100644
--- a/cicm_web/Areas/Admin/Controllers/InstructionSetExtensionsByProcessorController.cs
+++ b/cicm_web/Areas/Admin/Controllers/InstructionSetExtensionsByProcessorController.cs
@@ -156,5 +156,18 @@ namespace cicm_web.Areas.Admin.Controllers
         {
             return _context.InstructionSetExtensionsByProcessor.Any(e => e.Id == id);
         }
+
+        [AcceptVerbs("Get", "Post")]
+        public async Task<IActionResult> VerifyUnique(int processorId, int extensionId)
+        {
+            return
+                await _context.InstructionSetExtensionsByProcessor.FirstOrDefaultAsync(i =>
+                                                                                           i.ProcessorId ==
+                                                                                           processorId &&
+                                                                                           i.ExtensionId == extensionId)
+                    is null
+                    ? Json(true)
+                    : Json("The selected processor already has the selected extension.");
+        }
     }
 }
\ No newline at end of file
diff --git a/cicm_web/Areas/Admin/Views/InstructionSetExtensionsByProcessor/Create.cshtml b/cicm_web/Areas/Admin/Views/InstructionSetExtensionsByProcessor/Create.cshtml
index 2a570f82..1d1c8260 100644
--- a/cicm_web/Areas/Admin/Views/InstructionSetExtensionsByProcessor/Create.cshtml
+++ b/cicm_web/Areas/Admin/Views/InstructionSetExtensionsByProcessor/Create.cshtml
@@ -22,6 +22,9 @@
                         class="form-control"
                         asp-items="ViewBag.ProcessorId">
                 </select>
+                <span asp-validation-for="ProcessorId"
+                      class="text-danger">
+                </span>
             </div>
             <div class="form-group">
                 <label asp-for="Extension"
@@ -31,6 +34,9 @@
                         class="form-control"
                         asp-items="ViewBag.ExtensionId">
                 </select>
+                <span asp-validation-for="ExtensionId"
+                      class="text-danger">
+                </span>
             </div>
             <div class="form-group">
                 <input class="btn btn-primary"
@@ -43,4 +49,8 @@
             </div>
         </form>
     </div>
-</div>
\ No newline at end of file
+</div>
+
+@section Scripts {
+    @{ await Html.RenderPartialAsync("_ValidationScriptsPartial"); }
+}
\ No newline at end of file
diff --git a/cicm_web/Areas/Admin/Views/InstructionSetExtensionsByProcessor/Edit.cshtml b/cicm_web/Areas/Admin/Views/InstructionSetExtensionsByProcessor/Edit.cshtml
index 3c3eda32..9920317a 100644
--- a/cicm_web/Areas/Admin/Views/InstructionSetExtensionsByProcessor/Edit.cshtml
+++ b/cicm_web/Areas/Admin/Views/InstructionSetExtensionsByProcessor/Edit.cshtml
@@ -51,4 +51,8 @@
             </div>
         </form>
     </div>
-</div>
\ No newline at end of file
+</div>
+
+@section Scripts {
+    @{ await Html.RenderPartialAsync("_ValidationScriptsPartial"); }
+}
\ No newline at end of file
diff --git a/cicm_web/cicm_web.csproj b/cicm_web/cicm_web.csproj
index 31adc55e..508aadcc 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>3.0.99.497</Version>
+    <Version>3.0.99.503</Version>
     <Company>Canary Islands Computer Museum</Company>
     <Copyright>Copyright © 2003-2018 Natalia Portillo</Copyright>
     <Product>Canary Islands Computer Museum Website</Product>