diff --git a/app/models/comment.rb b/app/models/comment.rb
index 9415aaa55e..da15453ef3 100644
--- a/app/models/comment.rb
+++ b/app/models/comment.rb
@@ -107,7 +107,14 @@ def akismet_attributes
     # While we do have tag comments, those are from logged-in users with special
     # access granted by admins, so we never spam check them, unlike comments on
     # works or admin posts.
-    comment_type = ultimate_parent.is_a?(Work) ? "fanwork-comment" : "comment"
+    case ultimate_parent
+    when Work
+      comment_type = "fanwork-comment"
+      comment_post_modified_gmt = ultimate_parent.revised_at.iso8601
+    when AdminPost
+      comment_type = "comment"
+      comment_post_modified_gmt = ultimate_parent.created_at.iso8601
+    end
 
     if pseud_id.nil?
       user_role = "guest"
@@ -126,7 +133,8 @@ def akismet_attributes
       user_role: user_role,
       comment_author: comment_author,
       comment_author_email: comment_owner_email,
-      comment_content: comment_content
+      comment_content: comment_content,
+      comment_post_modified_gmt: comment_post_modified_gmt
     }
 
     attributes[:recheck_reason] = "edit" if will_save_change_to_edited_at? && will_save_change_to_comment_content?
diff --git a/spec/models/comment_spec.rb b/spec/models/comment_spec.rb
index d10be853ea..5242b09e8e 100644
--- a/spec/models/comment_spec.rb
+++ b/spec/models/comment_spec.rb
@@ -292,6 +292,10 @@ def queue_adapter_for_test
         it "has comment_type \"fanwork-comment\"" do
           expect(subject.akismet_attributes[:comment_type]).to eq("fanwork-comment")
         end
+
+        it "has comment_post_modified_gmt as the work's revision time" do
+          expect(subject.akismet_attributes[:comment_post_modified_gmt]).to eq(subject.ultimate_parent.revised_at.iso8601)
+        end
       end
 
       context "when the commentable is an admin post" do
@@ -300,6 +304,10 @@ def queue_adapter_for_test
         it "has comment_type \"comment\"" do
           expect(subject.akismet_attributes[:comment_type]).to eq("comment")
         end
+
+        it "has comment_post_modified_gmt as the admin post's creation time" do
+          expect(subject.akismet_attributes[:comment_post_modified_gmt]).to eq(subject.ultimate_parent.created_at.iso8601)
+        end
       end
 
       context "when the commentable is a comment" do
@@ -309,6 +317,10 @@ def queue_adapter_for_test
           it "has comment_type \"fanwork-comment\"" do
             expect(subject.akismet_attributes[:comment_type]).to eq("fanwork-comment")
           end
+
+          it "has comment_post_modified_gmt as the work's revision time" do
+            expect(subject.akismet_attributes[:comment_post_modified_gmt]).to eq(subject.ultimate_parent.revised_at.iso8601)
+          end
         end
 
         context "when the comment is on an admin post" do
@@ -317,6 +329,10 @@ def queue_adapter_for_test
           it "has comment_type \"comment\"" do
             expect(subject.akismet_attributes[:comment_type]).to eq("comment")
           end
+
+          it "has comment_post_modified_gmt as the admin post's creation time" do
+            expect(subject.akismet_attributes[:comment_post_modified_gmt]).to eq(subject.ultimate_parent.created_at.iso8601)
+          end
         end
       end
     end