--- a/lisp/nnimap.el
+++ b/lisp/nnimap.el
@@ -443,7 +443,7 @@ textual parts.")
 	    (setf (nnimap-greeting nnimap-object) greeting)
 	    (setf (nnimap-capabilities nnimap-object)
 		  (mapcar #'upcase
-			  (split-string capabilities)))
+			  (and capabilities (split-string capabilities))))
 	    (unless (gnus-string-match-p "[*.] PREAUTH" greeting)
 	      (if (not (setq credentials
 			     (if (eq nnimap-authenticator 'anonymous)