diff --git a/src/highlight.zsh b/src/highlight.zsh
index 273c03d..16c1937 100644
--- a/src/highlight.zsh
+++ b/src/highlight.zsh
@@ -17,7 +17,7 @@ _zsh_autosuggest_highlight_reset() {
 _zsh_autosuggest_highlight_apply() {
 	typeset -g _ZSH_AUTOSUGGEST_LAST_HIGHLIGHT
 
-	if (( $#POSTDISPLAY )); then
+	if [[ -v POSTDISPLAY && ${#POSTDISPLAY} -gt 0 ]]; then
 		typeset -g _ZSH_AUTOSUGGEST_LAST_HIGHLIGHT="$#BUFFER $(($#BUFFER + $#POSTDISPLAY)) $ZSH_AUTOSUGGEST_HIGHLIGHT_STYLE"
 		region_highlight+=("$_ZSH_AUTOSUGGEST_LAST_HIGHLIGHT")
 	else