diff --git a/src/main/scala/app/ControllerBase.scala b/src/main/scala/app/ControllerBase.scala
index 4b89776..1a39b2c 100644
--- a/src/main/scala/app/ControllerBase.scala
+++ b/src/main/scala/app/ControllerBase.scala
@@ -26,6 +26,9 @@
     }
   }
 
+  protected def NotFound()     = redirect("/")
+  protected def Unauthorized() = redirect("/")
+
 }
 
 case class Context(path: String, loginAccount: Option[Account])
\ No newline at end of file
diff --git a/src/main/scala/app/RepositoryViewerController.scala b/src/main/scala/app/RepositoryViewerController.scala
index 120081c..ed150c9 100644
--- a/src/main/scala/app/RepositoryViewerController.scala
+++ b/src/main/scala/app/RepositoryViewerController.scala
@@ -26,8 +26,10 @@
    */
   get("/:owner") {
     val owner = params("owner")
-
-    html.user(getAccountByUserName(owner).get, getRepositoriesOfUser(owner, servletContext))
+    getAccountByUserName(owner) match {
+      case Some(account) => html.user(account, getRepositoriesOfUser(owner, servletContext))
+      case None => NotFound()
+    }
   }
   
   /**
@@ -36,7 +38,7 @@
   get("/:owner/:repository")(readableRepository {
     val owner      = params("owner")
     val repository = params("repository")
-    
+
     fileList(owner, repository)
   })
   
@@ -98,8 +100,7 @@
         }, page, hasNext)
     }
   })
-  
-  
+
   /**
    * Displays the file content of the specified branch or commit.
    */
diff --git a/src/main/scala/app/SettingsController.scala b/src/main/scala/app/SettingsController.scala
index 32f54d0..dd7f52c 100644
--- a/src/main/scala/app/SettingsController.scala
+++ b/src/main/scala/app/SettingsController.scala
@@ -30,6 +30,7 @@
   get("/:owner/:repository/settings")(ownerOnly {
     val owner      = params("owner")
     val repository = params("repository")
+
     redirect("/%s/%s/settings/options".format(owner, repository))
   })
   
@@ -39,8 +40,11 @@
   get("/:owner/:repository/settings/options")(ownerOnly {
     val owner      = params("owner")
     val repository = params("repository")
-    
-    settings.html.options(getRepository(owner, repository, servletContext).get)
+
+    getRepository(owner, repository, servletContext) match {
+      case Some(r) => settings.html.options(r)
+      case None    => NotFound()
+    }
   })
   
   /**
@@ -62,8 +66,11 @@
   get("/:owner/:repository/settings/collaborators")(ownerOnly {
     val owner      = params("owner")
     val repository = params("repository")
-    
-    settings.html.collaborators(getCollaborators(owner, repository), getRepository(owner, repository, servletContext).get)
+
+    getRepository(owner, repository, servletContext) match {
+      case Some(r) => settings.html.collaborators(getCollaborators(owner, repository), r)
+      case None    => NotFound()
+    }
   })
 
   /**
@@ -72,6 +79,7 @@
   post("/:owner/:repository/settings/collaborators/add", collaboratorForm)(ownerOnly { form =>
     val owner      = params("owner")
     val repository = params("repository")
+
     addCollaborator(owner, repository, form.userName)
     redirect("/%s/%s/settings/collaborators".format(owner, repository))
   })
@@ -83,6 +91,7 @@
     val owner      = params("owner")
     val repository = params("repository")
     val userName   = params("name")
+
     removeCollaborator(owner, repository, userName)
     redirect("/%s/%s/settings/collaborators".format(owner, repository))
   })
diff --git a/src/main/scala/util/Authenticator.scala b/src/main/scala/util/Authenticator.scala
index 2696869..03facf5 100644
--- a/src/main/scala/util/Authenticator.scala
+++ b/src/main/scala/util/Authenticator.scala
@@ -2,12 +2,12 @@
 
 import app.ControllerBase
 import service._
+import org.scalatra._
 
 /**
  * Allows only the repository owner and administrators.
  */
 trait OwnerOnlyAuthenticator { self: ControllerBase =>
-
   protected def ownerOnly(action: => Any) = { authenticate(action) }
   protected def ownerOnly[T](action: T => Any) = (form: T) => authenticate({action(form)})
 
@@ -16,7 +16,7 @@
       context.loginAccount match {
         case Some(x) if(x.userType == AccountService.Administrator) => action
         case Some(x) if(request.getRequestURI.split("/")(1) == x.userName) => action
-        case _ => redirect("/signin")
+        case _ => Unauthorized()
       }
     }
   }
@@ -26,7 +26,6 @@
  * Allows only signed in users.
  */
 trait UsersOnlyAuthenticator { self: ControllerBase =>
-
   protected def usersOnly(action: => Any) = { authenticate(action) }
   protected def usersOnly[T](action: T => Any) = (form: T) => authenticate({action(form)})
 
@@ -34,7 +33,7 @@
     {
       context.loginAccount match {
         case Some(x) => action
-        case None    => redirect("/signin")
+        case None => Unauthorized()
       }
     }
   }
@@ -52,7 +51,7 @@
     {
       context.loginAccount match {
         case Some(x) if(x.userType == AccountService.Administrator) => action
-        case _ => redirect("/signin")
+        case _ => Unauthorized()
       }
     }
   }
@@ -62,7 +61,6 @@
  * Allows only collaborators and administrators.
  */
 trait WritableRepositoryAuthenticator { self: ControllerBase with RepositoryService =>
-
   protected def writableRepository(action: => Any) = { authenticate(action) }
   protected def writableRepository[T](action: T => Any) = (form: T) => authenticate({action(form)})
 
@@ -72,7 +70,7 @@
         case Some(x) if(x.userType == AccountService.Administrator) => action
         case Some(x) if(paths(1) == x.userName) => action
         case Some(x) if(getCollaborators(paths(1), paths(2)).contains(x.userName)) => action
-        case _ => redirect("/signin")
+        case _ => Unauthorized()
       }
   }
 }
@@ -81,7 +79,6 @@
  * Allows only the repository owner and administrators.
  */
 trait ReadableRepositoryAuthenticator { self: ControllerBase with RepositoryService =>
-
   protected def readableRepository(action: => Any) = { authenticate(action) }
   protected def readableRepository[T](action: T => Any) = (form: T) => authenticate({action(form)})
 
@@ -96,7 +93,7 @@
           case Some(x) if(x.userType == AccountService.Administrator) => action
           case Some(x) if(paths(1) == x.userName) => action
           case Some(x) if(getCollaborators(paths(1), paths(2)).contains(x.userName)) => action
-          case _ => redirect("/")
+          case _ => Unauthorized()
         }
       }
     }