diff --git a/app/assets/javascripts/index/note.js b/app/assets/javascripts/index/note.js
index e7790c904..15fedb1d1 100644
--- a/app/assets/javascripts/index/note.js
+++ b/app/assets/javascripts/index/note.js
@@ -52,20 +52,18 @@ OSM.Note = function (map) {
           OSM.loadSidebarContent(path, function () {
             initialize(path, id, moveToNote);
           });
+        },
+        error: function (xhr) {
+          $(form).find("#comment-error")
+            .text(xhr.responseText)
+            .prop("hidden", false);
+          updateButtons(form);
         }
       });
     });
 
     content.find("textarea").on("input", function (e) {
-      var form = e.target.form;
-
-      if ($(e.target).val() === "") {
-        $(form.close).val($(form.close).data("defaultActionText"));
-        $(form.comment).prop("disabled", true);
-      } else {
-        $(form.close).val($(form.close).data("commentActionText"));
-        $(form.comment).prop("disabled", false);
-      }
+      updateButtons(e.target.form);
     });
 
     content.find("textarea").val("").trigger("input");
@@ -84,6 +82,17 @@ OSM.Note = function (map) {
     if (callback) callback();
   }
 
+  function updateButtons(form) {
+    $(form).find("input[type=submit]").prop("disabled", false);
+    if ($(form.text).val() === "") {
+      $(form.close).val($(form.close).data("defaultActionText"));
+      $(form.comment).prop("disabled", true);
+    } else {
+      $(form.close).val($(form.close).data("commentActionText"));
+      $(form.comment).prop("disabled", false);
+    }
+  }
+
   function moveToNote() {
     var data = $(".details").data();
     if (!data) return;
diff --git a/app/views/notes/show.html.erb b/app/views/notes/show.html.erb
index d355d3e5f..a7baccf85 100644
--- a/app/views/notes/show.html.erb
+++ b/app/views/notes/show.html.erb
@@ -49,6 +49,8 @@
         <div class="mb-3">
           <textarea class="form-control" name="text" cols="40" rows="5" maxlength="2000"></textarea>
         </div>
+        <div id="comment-error" class="alert alert-danger p-2 mb-3" hidden>
+        </div>
         <div class="btn-wrapper">
           <% if current_user.moderator? -%>
             <%= submit_tag t(".hide"), :name => "hide", :class => "btn btn-light",
@@ -73,6 +75,8 @@
   <% else %>
     <form class="mb-3" action="#">
       <input type="hidden" name="text" value="" autocomplete="off">
+      <div id="comment-error" class="alert alert-danger p-2 mb-3" hidden>
+      </div>
       <div class="btn-wrapper">
         <% if @note.status != "hidden" and current_user and current_user.moderator? -%>
           <input type="submit" name="hide" value="<%= t(".hide") %>" class="btn btn-light" data-method="DELETE" data-url="<%= api_note_url(@note, "json") %>">
diff --git a/test/application_system_test_case.rb b/test/application_system_test_case.rb
index c2de02781..b170e74b1 100644
--- a/test/application_system_test_case.rb
+++ b/test/application_system_test_case.rb
@@ -21,4 +21,10 @@ class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
     Settings.reload!
     super
   end
+
+  private
+
+  def within_sidebar(&block)
+    within "#sidebar_content", &block
+  end
 end
diff --git a/test/system/note_comments_test.rb b/test/system/note_comments_test.rb
index 70cfc417c..7c830cc37 100644
--- a/test/system/note_comments_test.rb
+++ b/test/system/note_comments_test.rb
@@ -5,17 +5,21 @@ class NoteCommentsTest < ApplicationSystemTestCase
     note = create(:note_with_comments)
     visit note_path(note)
 
-    assert_no_button "Resolve"
-    assert_no_button "Comment"
-    assert_link "Log in to comment on this note", :href => login_path(:referer => note_path(note))
+    within_sidebar do
+      assert_no_button "Resolve"
+      assert_no_button "Comment"
+      assert_link "Log in to comment on this note", :href => login_path(:referer => note_path(note))
+    end
   end
 
   test "closed note has no login notice" do
     note = create(:note_with_comments, :closed)
     visit note_path(note)
 
-    assert_no_button "Reactivate"
-    assert_no_link "Log in to comment on this note"
+    within_sidebar do
+      assert_no_button "Reactivate"
+      assert_no_link "Log in to comment on this note"
+    end
   end
 
   def test_add_comment
@@ -24,19 +28,101 @@ class NoteCommentsTest < ApplicationSystemTestCase
     sign_in_as(user)
     visit note_path(note)
 
-    assert_no_content "Comment from #{user.display_name}"
-    assert_no_content "Some newly added note comment"
-    assert_button "Resolve"
-    assert_button "Comment", :disabled => true
+    within_sidebar do
+      assert_no_content "Comment from #{user.display_name}"
+      assert_no_content "Some newly added note comment"
+      assert_button "Resolve"
+      assert_button "Comment", :disabled => true
 
-    fill_in "text", :with => "Some newly added note comment"
+      fill_in "text", :with => "Some newly added note comment"
 
-    assert_button "Comment & Resolve"
-    assert_button "Comment", :disabled => false
+      assert_button "Comment & Resolve"
+      assert_button "Comment", :disabled => false
 
-    click_on "Comment"
+      click_on "Comment"
 
-    assert_content "Comment from #{user.display_name}"
-    assert_content "Some newly added note comment"
+      assert_content "Comment from #{user.display_name}"
+      assert_content "Some newly added note comment"
+    end
+  end
+
+  test "can't add a comment when blocked" do
+    note = create(:note_with_comments)
+    user = create(:user)
+    sign_in_as(user)
+    visit note_path(note)
+    block = create(:user_block, :user => user)
+
+    within_sidebar do
+      fill_in "text", :with => "Comment that won't be added while blocked"
+
+      assert_no_text "Comment from #{user.display_name}"
+      assert_no_text "Comment that won't be added while blocked"
+      assert_no_text "Your access to the API has been blocked"
+      assert_button "Comment & Resolve", :disabled => false
+      assert_button "Comment", :disabled => false
+
+      click_on "Comment"
+
+      assert_no_text "Comment from #{user.display_name}"
+      assert_no_text "Comment that won't be added while blocked"
+      assert_text "Your access to the API has been blocked"
+      assert_button "Comment & Resolve", :disabled => false
+      assert_button "Comment", :disabled => false
+
+      block.revoke! block.creator
+
+      click_on "Comment"
+
+      assert_text "Comment from #{user.display_name}"
+      assert_text "Comment that won't be added while blocked"
+      assert_no_text "Your access to the API has been blocked"
+    end
+  end
+
+  test "can't resolve a note when blocked" do
+    note = create(:note_with_comments)
+    user = create(:user)
+    sign_in_as(user)
+    visit note_path(note)
+    create(:user_block, :user => user)
+
+    within_sidebar do
+      assert_text "Unresolved note"
+      assert_no_text "Resolved note"
+      assert_no_text "Your access to the API has been blocked"
+      assert_button "Resolve", :disabled => false
+      assert_button "Comment", :disabled => true
+
+      click_on "Resolve"
+
+      assert_text "Unresolved note"
+      assert_no_text "Resolved note"
+      assert_text "Your access to the API has been blocked"
+      assert_button "Resolve", :disabled => false
+      assert_button "Comment", :disabled => true
+    end
+  end
+
+  test "can't reactivate a note when blocked" do
+    note = create(:note_with_comments, :closed)
+    user = create(:user)
+    sign_in_as(user)
+    visit note_path(note)
+    create(:user_block, :user => user)
+
+    within_sidebar do
+      assert_no_text "Unresolved note"
+      assert_text "Resolved note"
+      assert_no_text "Your access to the API has been blocked"
+      assert_button "Reactivate", :disabled => false
+
+      click_on "Reactivate"
+
+      assert_no_text "Unresolved note"
+      assert_text "Resolved note"
+      assert_text "Your access to the API has been blocked"
+      assert_button "Reactivate", :disabled => false
+    end
   end
 end