diff --git a/simple-comment-markup.el b/simple-comment-markup.el
index 9d444f6..3a79679 100644
--- a/simple-comment-markup.el
+++ b/simple-comment-markup.el
@@ -158,7 +158,7 @@ This must not include any capturing groups."
                         (not
                          (re-search-forward
                           (rx point (syntax comment-start)) nil t))))))))))
-    (when multiline
+    (when (and multiline (< markup-start markup-end))
       (put-text-property markup-start markup-end 'font-lock-multiline t))
     (set-match-data (and markup-start (list markup-start markup-end)))))