1 files changed, 11 insertions, 11 deletions

diff --git a/lisp/icomplete.el b/lisp/icomplete.el
index a9719651957..97a14b12891 100644
--- a/lisp/icomplete.el
+++ b/lisp/icomplete.el
@@ -333,23 +333,23 @@ are exhibited within the square braces.)"
                  (window-width)))
              (prefix-len
               ;; Find the common prefix among `comps'.
-              (if (eq t (compare-strings (car comps) nil (length most)
-                                         most nil nil completion-ignore-case))
-                  ;; Common case.
-                  (length most)
-                ;; Else, use try-completion.
-                (let ((comps-prefix (try-completion "" comps)))
-                  (and (stringp comps-prefix)
-                       (length comps-prefix)))))
+              ;; We can't use the optimization below because its assumptions
+              ;; aren't always true, e.g. when completion-cycling (bug#10850):
+              ;; (if (eq t (compare-strings (car comps) nil (length most)
+              ;;                         most nil nil completion-ignore-case))
+              ;;     ;; Common case.
+              ;;     (length most)
+              ;; Else, use try-completion.
+              (let ((comps-prefix (try-completion "" comps)))
+                (and (stringp comps-prefix)
+                     (length comps-prefix)))) ;;)
 
              prospects most-is-exact comp limit)
         (if (eq most-try t) ;; (or (null (cdr comps))
             (setq prospects nil)
           (while (and comps (not limit))
             (setq comp
-                  (if (and prefix-len (<= prefix-len (length (car comps))))
-                      (substring (car comps) prefix-len)
-                    (car comps))
+                  (if prefix-len (substring (car comps) prefix-len) (car comps))
                   comps (cdr comps))
             (cond ((string-equal comp "") (setq most-is-exact t))
                   ((member comp prospects))