diff --git a/cmd/mirror_edit.go b/cmd/mirror_edit.go
index 6e07d066..7c738114 100644
--- a/cmd/mirror_edit.go
+++ b/cmd/mirror_edit.go
@@ -55,6 +55,10 @@ func aptlyMirrorEdit(cmd *commander.Command, args []string) error {
 		return fmt.Errorf("unable to edit: flat mirrors don't support udebs")
 	}
 
+	if repo.IsFlat() && repo.DownloadAppStream {
+		return fmt.Errorf("unable to edit: flat mirrors don't support AppStream (DEP-11) metadata")
+	}
+
 	if repo.Filter != "" {
 		_, err = query.Parse(repo.Filter)
 		if err != nil {
diff --git a/deb/remote.go b/deb/remote.go
index aa4f1151..a1a79d68 100644
--- a/deb/remote.go
+++ b/deb/remote.go
@@ -116,6 +116,9 @@ func NewRemoteRepo(name string, archiveRoot string, distribution string, compone
 		if result.DownloadUdebs {
 			return nil, fmt.Errorf("debian-installer udebs aren't supported for flat repos")
 		}
+		if result.DownloadAppStream {
+			return nil, fmt.Errorf("AppStream (DEP-11) metadata isn't supported for flat repos")
+		}
 		result.Components = nil
 	}
 
diff --git a/deb/remote_test.go b/deb/remote_test.go
index 95b5d181..d4558c5d 100644
--- a/deb/remote_test.go
+++ b/deb/remote_test.go
@@ -123,6 +123,9 @@ func (s *RemoteRepoSuite) TestFlatCreation(c *C) {
 
 	_, err := NewRemoteRepo("fl", "http://some.repo/", "./", []string{"main"}, []string{}, false, false, false, false)
 	c.Check(err, ErrorMatches, "components aren't supported for flat repos")
+
+	_, err = NewRemoteRepo("fl", "http://some.repo/", "./", []string{}, []string{}, false, false, false, true)
+	c.Check(err, ErrorMatches, "AppStream \\(DEP-11\\) metadata isn't supported for flat repos")
 }
 
 func (s *RemoteRepoSuite) TestString(c *C) {
@@ -139,8 +142,7 @@ func (s *RemoteRepoSuite) TestString(c *C) {
 	s.repo.DownloadAppStream = true
 	c.Check(s.repo.String(), Equals, "[yandex]: http://mirror.yandex.ru/debian/ squeeze [src] [udeb] [installer] [appstream]")
 
-	s.flat.DownloadAppStream = true
-	c.Check(s.flat.String(), Equals, "[exp42]: http://repos.express42.com/virool/precise/ ./ [src] [appstream]")
+	// AppStream is not supported for flat repos, so no flat test here
 }
 
 func (s *RemoteRepoSuite) TestAppStreamPaths(c *C) {