diff --git a/src/main/scala/app/RepositorySettingsController.scala b/src/main/scala/app/RepositorySettingsController.scala
index 5793293..6647518 100644
--- a/src/main/scala/app/RepositorySettingsController.scala
+++ b/src/main/scala/app/RepositorySettingsController.scala
@@ -24,7 +24,7 @@
   case class OptionsForm(repositoryName: String, description: Option[String], defaultBranch: String, isPrivate: Boolean)
   
   val optionsForm = mapping(
-    "repositoryName" -> trim(label("Description"    , text(required, maxlength(40), identifier))), // TODO unique checking
+    "repositoryName" -> trim(label("Description"    , text(required, maxlength(40), identifier, renameRepositoryName))),
     "description"    -> trim(label("Description"    , optional(text()))),
     "defaultBranch"  -> trim(label("Default Branch" , text(required, maxlength(100)))),
     "isPrivate"      -> trim(label("Repository Type", boolean()))
@@ -209,4 +209,16 @@
       }
   }
 
+  /**
+   * Duplicate check for the rename repository name.
+   */
+  private def renameRepositoryName: Constraint = new Constraint(){
+    override def validate(name: String, value: String, params: Map[String, String], messages: Messages): Option[String] =
+      params.get("repository").filter(_ != value).flatMap { _ =>
+        params.get("owner").flatMap { userName =>
+          getRepositoryNamesOfUser(userName).find(_ == value).map(_ => "Repository already exists.")
+        }
+      }
+  }
+
 }
\ No newline at end of file
diff --git a/src/main/twirl/settings/options.scala.html b/src/main/twirl/settings/options.scala.html
index ed65ed5..5c76578 100644
--- a/src/main/twirl/settings/options.scala.html
+++ b/src/main/twirl/settings/options.scala.html
@@ -12,6 +12,7 @@
           <fieldset>
             <label for="repositoryName" class="strong">Repository Name:</label>
             <input type="text" name="repositoryName" id="repositoryName" value="@repository.name"/>
+            <span id="error-repositoryName" class="error"></span>
           </fieldset>
           <fieldset class="margin">
             <label for="description" class="strong">Description:</label>