diff --git a/zsh-syntax-highlighting.zsh b/zsh-syntax-highlighting.zsh
index 9f8fe48..4295c93 100644
--- a/zsh-syntax-highlighting.zsh
+++ b/zsh-syntax-highlighting.zsh
@@ -155,18 +155,7 @@ _zsh_highlight()
         # C structs, so that none of the previous case patterns will match.
         #
         # In either case, fall back to a version check.
-        #
-        # The memo= feature was added to zsh in commit zsh-5.8-172-gdd6e702ee.
-        # The version number at the time was 5.8.0.2-dev (see Config/version.mk).
-        # Therefore, on zsh master 5.8.0.3 and newer the memo= feature is available.
-        # However, there's also the zsh 5.8.1 release, which doesn't have the
-        # memo= feature.
-        #
-        # On zsh master 5.8.0.2 between the aforementioned commit and the
-        # first Config/version.mk bump after it (zsh-5.8-607-g75c1edde5, the
-        # bump to 5.8.1.1-dev following the backport to master of the bump
-        # to 5.8.1), this condition will false negative.
-        if is-at-least 5.8.1.1 $ZSH_VERSION.0.0; then
+        if is-at-least 5.9; then
           integer -gr zsh_highlight__memo_feature=1
         else
           integer -gr zsh_highlight__memo_feature=0
@@ -415,9 +404,7 @@ _zsh_highlight_call_widget()
 #    We check this with a plain version number check, since a functional check,
 #    as done by _zsh_highlight, can only be done from inside a widget
 #    function — a catch-22.
-#
-#    See _zsh_highlight for the magic version number.
-if is-at-least 5.8.1.1 $ZSH_VERSION.0.0 && _zsh_highlight__function_callable_p add-zle-hook-widget
+if is-at-least 5.9 && _zsh_highlight__function_callable_p add-zle-hook-widget
 then
   autoload -U add-zle-hook-widget
   _zsh_highlight__zle-line-finish() {