diff --git a/lisp/net/mailcap.el b/lisp/net/mailcap.el
index ed35c220ec5..031d8e1ff05 100644
--- a/lisp/net/mailcap.el
+++ b/lisp/net/mailcap.el
@@ -164,6 +164,10 @@ is consulted."
       (non-viewer . t)
       (type   . "application/zip")
       ("copiousoutput"))
+     ("pdf"
+      (viewer . pdf-view-mode)
+      (type . "application/pdf")
+      (test . (eq window-system 'x)))
      ("pdf"
       (viewer . doc-view-mode)
       (type . "application/pdf")