diff --git a/printer/format/format-e.lsp b/printer/format/format-e.lsp
index c25f54bff27022b2beae17912f260d91469a5a64..7eea2a6420d33e08f697ca2f1f26b6b6e853b1e7 100644
--- a/printer/format/format-e.lsp
+++ b/printer/format/format-e.lsp
@@ -313,6 +313,9 @@
           collect (list x s s2)))
   nil)
 
+;;; undefined behaviour: the format string is "~,2,,4E": d is 2 and k
+;;; is 4, but k (4) is not strictly less than d+2 (4).
+#+(or)
 (deftest format.e.20
   (let ((fn (formatter "~,2,,4e")))
     (loop for x in '(1/20 0.05s0 0.05f0 0.05d0 0.05l0)