$ echo 1 2 3 | sed '1ifoobar'     # BSD sed
sed: 1: "1ifoobar": command i expects \ followed by text

$ echo 1 2 3 | gsed '1ifoobar'   # GNU sed
foobar
1 2 3

$ echo 1 2 3 | sed '1i\
foobar '          # BSD sed again
foobar 1 2 3

sed() {
  gsed "$@"
}

diff --git a/liblist.sh b/liblist.sh
index d3a2144..f9bb2d2 100644
--- a/liblist.sh
+++ b/liblist.sh
@@ -75,7 +75,8 @@ list_push_back () {
 #
 list_insert () {
     test "$#" -ne 3 && return 1
-    i="$2"; [ "$i" != '$' ] &&  i=$((i+1)); echo "$3" | sed "${i}i${1}"
+    i="$2"; [ "$i" != '$' ] &&  i=$((i+1)); echo "$3" | sed "${i}i\\
+${1}"
 }
 
 ##
diff --git a/liblist_unsafe.sh b/liblist_unsafe.sh
index 4ae9951..2da93d5 100644
--- a/liblist_unsafe.sh
+++ b/liblist_unsafe.sh
@@ -79,7 +79,8 @@ list_push_back () {
 #
 list_insert () {
     test "$#" -ne 3 && return 1; i="$3"; [ "$i" != '$' ] &&  i=$((i+1))
-    eval "$1=\"\$(echo \"\$$1\" | sed \"${i}i${2}\")\""
+    eval "$1=\"\$(echo \"\$$1\" | sed \"${i}i\\
+${2}\")\""
 }
 
 ##