diff --git a/util/nocasemaps/nocase.go b/util/nocasemaps/nocase.go
index eaaaef559..4da7e6c9b 100644
--- a/util/nocasemaps/nocase.go
+++ b/util/nocasemaps/nocase.go
@@ -74,6 +74,22 @@ func Delete[K ~string, V any](m map[K]V, k K) {
 	delete(m, K(appendToLower(a[:0], string(k))))
 }
 
+// AppendSliceElem is equivalent to:
+//
+//	append(m[strings.ToLower(k)], v)
+func AppendSliceElem[K ~string, S []E, E any](m map[K]S, k K, vs ...E) {
+	// if the key is already lowercased
+	if isLowerASCII(string(k)) {
+		m[k] = append(m[k], vs...)
+		return
+	}
+
+	// if key needs to become lowercase, uses appendToLower
+	var a [stackArraySize]byte
+	s := appendToLower(a[:0], string(k))
+	m[K(s)] = append(m[K(s)], vs...)
+}
+
 func isLowerASCII(s string) bool {
 	for i := 0; i < len(s); i++ {
 		if c := s[i]; c >= utf8.RuneSelf || ('A' <= c && c <= 'Z') {
diff --git a/util/nocasemaps/nocase_test.go b/util/nocasemaps/nocase_test.go
index 310f82889..7d99f38ff 100644
--- a/util/nocasemaps/nocase_test.go
+++ b/util/nocasemaps/nocase_test.go
@@ -45,6 +45,23 @@ func Test(t *testing.T) {
 	c.Assert(m, qt.DeepEquals, map[string]int{"hello": 2, "baz": 5})
 	Delete(m, "BAZ")
 	c.Assert(m, qt.DeepEquals, map[string]int{"hello": 2})
+	// test cases for AppendSliceElem with int slices
+	appendTestInt := make(map[string][]int)
+	Set(appendTestInt, "firsT", []int{7})
+	c.Assert(appendTestInt, qt.DeepEquals, map[string][]int{"first": {7}})
+	AppendSliceElem(appendTestInt, "firsT", 77)
+	c.Assert(appendTestInt, qt.DeepEquals, map[string][]int{"first": {7, 77}})
+	Set(appendTestInt, "SeCOnd", []int{56})
+	c.Assert(appendTestInt, qt.DeepEquals, map[string][]int{"first": {7, 77}, "second": {56}})
+	AppendSliceElem(appendTestInt, "seCOnd", 563, 23)
+	c.Assert(appendTestInt, qt.DeepEquals, map[string][]int{"first": {7, 77}, "second": {56, 563, 23}})
+	// test cases for AppendSliceElem with string slices
+	appendTestString := make(map[string][]string)
+	Set(appendTestString, "firsTSTRING", []string{"hi"})
+	c.Assert(appendTestString, qt.DeepEquals, map[string][]string{"firststring": {"hi"}})
+	AppendSliceElem(appendTestString, "firsTSTRING", "hello", "bye")
+	c.Assert(appendTestString, qt.DeepEquals, map[string][]string{"firststring": {"hi", "hello", "bye"}})
+
 }
 
 var lowerTests = []struct{ in, want string }{