diff --git a/history-substring-search.zsh b/history-substring-search.zsh
index 9434a2d..c1e51e0 100644
--- a/history-substring-search.zsh
+++ b/history-substring-search.zsh
@@ -140,7 +140,7 @@ HISTORY_SUBSTRING_SEARCH_GLOBBING_FLAGS='i'
 # the main ZLE widgets
 #-----------------------------------------------------------------------------
 
-history-substring-search-up() {
+function history-substring-search-up() {
   _history-substring-search-begin
 
   _history-substring-search-up-history ||
@@ -150,7 +150,7 @@ history-substring-search-up() {
   _history-substring-search-end
 }
 
-history-substring-search-down() {
+function history-substring-search-down() {
   _history-substring-search-begin
 
   _history-substring-search-down-history ||
@@ -278,7 +278,7 @@ if [[ $+functions[_zsh_highlight] -eq 0 ]]; then
   #-------------->8------------------->8------------------->8-----------------
 fi
 
-_history-substring-search-begin() {
+function _history-substring-search-begin() {
   _history_substring_search_move_cursor_eol=false
   _history_substring_search_query_highlight=
 
@@ -326,7 +326,7 @@ _history-substring-search-begin() {
   fi
 }
 
-_history-substring-search-end() {
+function _history-substring-search-end() {
   _history_substring_search_result=$BUFFER
 
   # move the cursor to the end of the command line
@@ -358,7 +358,7 @@ _history-substring-search-end() {
   true
 }
 
-_history-substring-search-up-buffer() {
+function _history-substring-search-up-buffer() {
   #
   # Check if the UP arrow was pressed to move the cursor within a multi-line
   # buffer. This amounts to three tests:
@@ -387,7 +387,7 @@ _history-substring-search-up-buffer() {
   false
 }
 
-_history-substring-search-down-buffer() {
+function _history-substring-search-down-buffer() {
   #
   # Check if the DOWN arrow was pressed to move the cursor within a multi-line
   # buffer. This amounts to three tests:
@@ -416,7 +416,7 @@ _history-substring-search-down-buffer() {
   false
 }
 
-_history-substring-search-up-history() {
+function _history-substring-search-up-history() {
   #
   # Behave like up in ZSH, except clear the $BUFFER
   # when beginning of history is reached like in Fish.
@@ -438,7 +438,7 @@ _history-substring-search-up-history() {
   false
 }
 
-_history-substring-search-down-history() {
+function _history-substring-search-down-history() {
   #
   # Behave like down-history in ZSH, except clear the
   # $BUFFER when end of history is reached like in Fish.
@@ -461,7 +461,7 @@ _history-substring-search-down-history() {
   false
 }
 
-_history-substring-search-up-search() {
+function _history-substring-search-up-search() {
   _history_substring_search_move_cursor_eol=true
 
   #
@@ -534,7 +534,7 @@ _history-substring-search-up-search() {
   fi
 }
 
-_history-substring-search-down-search() {
+function _history-substring-search-down-search() {
   _history_substring_search_move_cursor_eol=true
 
   #