diff --git a/lisp/icomplete.el b/lisp/icomplete.el
index 4e546807b7..ec11cbffce 100644
--- a/lisp/icomplete.el
+++ b/lisp/icomplete.el
@@ -701,19 +701,23 @@ icomplete-completions
 				((< compare (+ 2 (string-width ellipsis))) most)
 				(t (concat ellipsis (substring most compare))))
 			       close-bracket)))
+             (vertical (string-match "\n" icomplete-separator))
 	     ;;"-prospects" - more than one candidate
-	     (prospects-len (+ (string-width
-				(or determ (concat open-bracket close-bracket)))
-			       (string-width icomplete-separator)
-			       (+ 2 (string-width ellipsis)) ;; take {…} into account
-			       (string-width (buffer-string))))
+	     (prospects-len (unless vertical
+                              (+ (string-width
+				  (or determ (concat open-bracket close-bracket)))
+			         (string-width icomplete-separator)
+			         (+ 2 (string-width ellipsis)) ;; take {…} into account
+			         (string-width (buffer-string)))))
              (prospects-max
-              ;; Max total length to use, including the minibuffer content.
-              (* (+ icomplete-prospects-height
-                    ;; If the minibuffer content already uses up more than
-                    ;; one line, increase the allowable space accordingly.
-                    (/ prospects-len (window-width)))
-                 (window-width)))
+              (if vertical
+                  icomplete-prospects-height
+                ;; Max total length to use, including the minibuffer content.
+                (* (+ icomplete-prospects-height
+                      ;; If the minibuffer content already uses up more than
+                      ;; one line, increase the allowable space accordingly.
+                      (/ prospects-len (window-width)))
+                   (window-width))))
              ;; Find the common prefix among `comps'.
              ;; We can't use the optimization below because its assumptions
              ;; aren't always true, e.g. when completion-cycling (bug#10850):
@@ -730,7 +734,9 @@ icomplete-completions
                    ;; is already displayed via `most'.
                    (string-prefix-p prefix most t)
                    (length prefix))) ;;)
-	     prospects comp limit)
+             (limit (when vertical
+                      (> (length comps) prospects-max)))
+	     prospects comp)
 	(if (or (eq most-try t) (not (consp (cdr comps))))
 	    (setq prospects nil)
 	  (when (member name comps)
@@ -753,17 +759,24 @@ icomplete-completions
 	    ;; completion field.
 	    (setq determ (concat open-bracket "" close-bracket)))
 	  ;; Compute prospects for display.
-	  (while (and comps (not limit))
-	    (setq comp
-		  (if prefix-len (substring (car comps) prefix-len) (car comps))
-		  comps (cdr comps))
-	    (setq prospects-len
-                  (+ (string-width comp)
-		     (string-width icomplete-separator)
-		     prospects-len))
-	    (if (< prospects-len prospects-max)
-		(push comp prospects)
-	      (setq limit t))))
+	  (if vertical
+              (while (and comps (> prospects-max 0))
+                (setq prospects-max (1- prospects-max))
+                (push (if prefix-len
+                          (substring (pop comps) prefix-len)
+                        (pop comps))
+                      prospects))
+            (while (and comps (not limit))
+	      (setq comp
+		    (if prefix-len (substring (car comps) prefix-len) (car comps))
+		    comps (cdr comps))
+	      (setq prospects-len
+                    (+ (string-width comp)
+		       (string-width icomplete-separator)
+		       prospects-len))
+	      (if (< prospects-len prospects-max)
+		  (push comp prospects)
+	        (setq limit t)))))
 	(setq prospects (nreverse prospects))
 	;; Decorate first of the prospects.
 	(when prospects