diff --git a/app/controllers/groups/milestones_controller.rb b/app/controllers/groups/milestones_controller.rb
index 9d5a28e8d4df30f0d4ab196f169d3fdc088b23e4..506484932ccb5cce799567816268fc280d991dc3 100644
--- a/app/controllers/groups/milestones_controller.rb
+++ b/app/controllers/groups/milestones_controller.rb
@@ -58,7 +58,7 @@ class Groups::MilestonesController < Groups::ApplicationController
 
   def render_new_with_error(empty_project_ids)
     @milestone = Milestone.new(milestone_params)
-    @milestone.errors.add(:project_id, "Please select at least one project.") if empty_project_ids
+    @milestone.errors.add(:base, "Please select at least one project.") if empty_project_ids
     render :new
   end
 
diff --git a/app/views/groups/milestones/new.html.haml b/app/views/groups/milestones/new.html.haml
index 23d438b2aa12c3000a13d81417d744045dd4df7a..0dfaf74399207507bfe2441f81fb01cc65bc5df3 100644
--- a/app/views/groups/milestones/new.html.haml
+++ b/app/views/groups/milestones/new.html.haml
@@ -34,7 +34,7 @@
         = f.label :projects, "Projects", class: "control-label"
         .col-sm-10
           = f.collection_select :project_ids, @group.projects.non_archived, :id, :name,
-            { selected: @group.projects.non_archived.pluck(:id) }, multiple: true, class: 'select2'
+            { selected: @group.projects.non_archived.pluck(:id) }, required: true, multiple: true, class: 'select2'
 
     .col-md-6
       .form-group
diff --git a/changelogs/unreleased/milestone-project-require.yml b/changelogs/unreleased/milestone-project-require.yml
new file mode 100644
index 0000000000000000000000000000000000000000..e43033541c78aea7f76a2561c1b730123ec5e291
--- /dev/null
+++ b/changelogs/unreleased/milestone-project-require.yml
@@ -0,0 +1,4 @@
+---
+title: Require projects before creating milestone.
+merge_request: 7301
+author: gfyoung