diff --git a/eldoc-box.el b/eldoc-box.el
index 7b7582e..63999e7 100644
--- a/eldoc-box.el
+++ b/eldoc-box.el
@@ -331,6 +331,10 @@ Checkout `lsp-ui-doc--make-frame', `lsp-ui-doc--move-frame'."
       (set-window-dedicated-p window t)
       (redirect-frame-focus frame (frame-parent frame))
       (set-face-attribute 'internal-border frame :inherit 'eldoc-box-border)
+      (when (facep 'child-frame-border)
+        (set-face-background 'child-frame-border
+                             (face-attribute 'eldoc-box-border :background)
+                             frame))
       ;; set size
       (eldoc-box--update-childframe-geometry frame window)
       (setq eldoc-box--frame frame)