diff --git a/src/index.js b/src/index.js
index 3c9fc987..9c4b93c1 100644
--- a/src/index.js
+++ b/src/index.js
@@ -366,7 +366,8 @@ class Dayjs {
   locale(preset, object) {
     if (!preset) return this.$L
     const that = this.clone()
-    that.$L = parseLocale(preset, object, true)
+    const nextLocaleName = parseLocale(preset, object, true)
+    if (nextLocaleName) that.$L = nextLocaleName
     return that
   }
 
diff --git a/test/locale.test.js b/test/locale.test.js
index 1ac0aa9c..48e1f566 100644
--- a/test/locale.test.js
+++ b/test/locale.test.js
@@ -121,3 +121,12 @@ describe('Instance locale inheritance', () => {
     expect(dayjs.locale()).toBe(moment.locale())
   })
 })
+
+
+it('Not supported locale string fallback to previous one', () => {
+  const D = dayjs()
+  const DFormat = D.format()
+  const D2 = D.locale('not_supported_locale_string')
+  const D2Format = D2.format()
+  expect(DFormat).toBe(D2Format)
+})