diff --git a/src/index.js b/src/index.js
index 8c919b0d8..c965dd004 100644
--- a/src/index.js
+++ b/src/index.js
@@ -12,12 +12,17 @@ const parseLocale = (preset, object, isLocal) => {
   let l
   if (!preset) return L
   if (typeof preset === 'string') {
-    if (Ls[preset]) {
-      l = preset
+    const presetLower = preset.toLowerCase()
+    if (Ls[presetLower]) {
+      l = presetLower
     }
     if (object) {
-      Ls[preset] = object
-      l = preset
+      Ls[presetLower] = object
+      l = presetLower
+    }
+    const presetSplit = preset.split('-')
+    if (!l && presetSplit.length > 1) {
+      return parseLocale(presetSplit[0])
     }
   } else {
     const { name } = preset
diff --git a/test/plugin/localizedFormat.test.js b/test/plugin/localizedFormat.test.js
index 1c7a89e14..da5b219e0 100644
--- a/test/plugin/localizedFormat.test.js
+++ b/test/plugin/localizedFormat.test.js
@@ -96,6 +96,16 @@ it('Uses the localized lowercase formats if defined', () => {
   ['l', 'll', 'lll', 'llll'].forEach(option => expect(znDate.format(option)).toBe(znDate.format(znCn.formats[option])))
 })
 
+it('Uses fallback to xx if xx-yy not available', () => {
+  expect(dayjs('2019-02-01').locale('en-yy').format('MMMM'))
+    .toBe('February')
+})
+
+it('Uses xx-yy if xx-YY is provided', () => {
+  expect(dayjs('2019-02-01').locale('es-US').format('MMMM'))
+    .toBe('febrero')
+})
+
 it('Uses the localized uppercase formats as a base for lowercase formats, if not defined', () => {
   const date = new Date()
   const spanishDate = dayjs(date, { locale: es });