diff --git a/lib/linter.rb b/lib/linter.rb
index f3254ffdfc..63d9e807bf 100644
--- a/lib/linter.rb
+++ b/lib/linter.rb
@@ -125,6 +125,7 @@ def check_releases
       errors[release] << invalid_url_message(release.post)  if release.post_url_invalid?
       errors[release] << "release date and post date do not match"  if release.date_mismatch?
       errors[release] << missing_post_message(release.post_filename)  if release.post_missing?
+      errors[release] << "release date is a string, not a Date object"  if release.date.is_a?(String)
     end
   end
 
diff --git a/test/test_linter_invalid_release_data.rb b/test/test_linter_invalid_release_data.rb
index 24efe49272..b57176760f 100644
--- a/test/test_linter_invalid_release_data.rb
+++ b/test/test_linter_invalid_release_data.rb
@@ -57,4 +57,15 @@
     create_file("_data/releases.yml", content)
     _(linter_output).must_match "release date and post date do not match"
   end
+
+  it "reports release data with wrong date format" do
+    content = <<~YAML
+      - version: 2.7.1
+        date: '2020-01-01'
+        post: /en/news/2020/01/01/post/
+    YAML
+
+    create_file("_data/releases.yml", content)
+    _(linter_output).must_match "release date is a string, not a Date object"
+  end
 end