diff --git a/lib/pleroma/web/mastodon_api/views/instance_view.ex b/lib/pleroma/web/mastodon_api/views/instance_view.ex
index 18c6c0f80..0dc7a5fea 100644
--- a/lib/pleroma/web/mastodon_api/views/instance_view.ex
+++ b/lib/pleroma/web/mastodon_api/views/instance_view.ex
@@ -123,12 +123,17 @@ defmodule Pleroma.Web.MastodonAPI.InstanceView do
             host in exclusions or not Map.has_key?(@block_severities, rule)
           end)
           |> Enum.map(fn {host, reason} ->
-            %{
+            domain_block = %{
               domain: host,
               digest: :crypto.hash(:sha256, host) |> Base.encode16(case: :lower),
-              severity: Map.get(@block_severities, rule),
-              comment: reason
+              severity: Map.get(@block_severities, rule)
             }
+
+            if not_empty_string(reason) do
+              Map.put(domain_block, :comment, reason)
+            else
+              domain_block
+            end
           end)
         end)
         |> List.flatten()
diff --git a/test/pleroma/web/mastodon_api/controllers/instance_controller_test.exs b/test/pleroma/web/mastodon_api/controllers/instance_controller_test.exs
index e0c9091e0..461b46066 100644
--- a/test/pleroma/web/mastodon_api/controllers/instance_controller_test.exs
+++ b/test/pleroma/web/mastodon_api/controllers/instance_controller_test.exs
@@ -171,6 +171,22 @@ defmodule Pleroma.Web.MastodonAPI.InstanceControllerTest do
              ] == json_response_and_validate_schema(conn, 200)
     end
 
+    test "omits comment field if comment is empty", %{conn: conn} do
+      clear_config([:mrf_simple, :reject], ["fediverse.pl"])
+
+      conn = get(conn, "/api/v1/instance/domain_blocks")
+
+      assert [
+               %{
+                 "digest" => "55e3f44aefe7eb022d3b1daaf7396cabf7f181bf6093c8ea841e30c9fc7d8226",
+                 "domain" => "fediverse.pl",
+                 "severity" => "suspend"
+               } = domain_block
+             ] = json_response_and_validate_schema(conn, 200)
+
+      refute Map.has_key?(domain_block, "comment")
+    end
+
     test "returns empty array if mrf transparency is disabled", %{conn: conn} do
       clear_config([:mrf, :transparency], false)