diff --git a/__tests__/slug.test.ts b/__tests__/slug.test.ts
index 05e2201..ae516b8 100644
--- a/__tests__/slug.test.ts
+++ b/__tests__/slug.test.ts
@@ -35,6 +35,11 @@ test('slug: a number', () => {
   test_slug_cs('4.2', '4.2')
 })
 
+test('slug: an underscore', () => {
+  test_slug('An_Underscore', 'an_underscore')
+  test_slug_cs('An_Underscore', 'An_Underscore')
+})
+
 test('slug: special character', () => {
   test_slug('feat-(!è§-character', 'feat------character')
   test_slug_cs('feat-(!è§-character', 'feat------character')
diff --git a/__tests__/slugref.test.ts b/__tests__/slugref.test.ts
index f8b08bf..b9b2351 100644
--- a/__tests__/slugref.test.ts
+++ b/__tests__/slugref.test.ts
@@ -25,6 +25,11 @@ test('slug_ref: a fix branch', () => {
   test_slugref_cs('refs/heads/fix/issue_number', 'fix-issue_number')
 })
 
+test('slug_ref: an underscore', () => {
+  test_slugref('refs/heads/An_Underscore', 'an_underscore')
+  test_slugref_cs('refs/heads/An_Underscore', 'An_Underscore')
+})
+
 test('slug_ref: a simple tag', () => {
   test_slugref('refs/tags/v1.0.0', 'v1.0.0')
   test_slugref_cs('refs/tags/v1.0.0', 'v1.0.0')
diff --git a/__tests__/slugurl.test.ts b/__tests__/slugurl.test.ts
index 9eb799b..5884149 100644
--- a/__tests__/slugurl.test.ts
+++ b/__tests__/slugurl.test.ts
@@ -35,6 +35,11 @@ test('slug_url: a number', () => {
   test_slugurl_cs('4.2', '4-2')
 })
 
+test('slug_url: an underscore', () => {
+  test_slugurl('An_Underscore', 'an-underscore')
+  test_slugurl_cs('An_Underscore', 'An-Underscore')
+})
+
 test('slug_url: trailing', () => {
   test_slugurl('.path.to.', 'path-to')
   test_slugurl_cs('.path.to.', 'path-to')
diff --git a/__tests__/slugurlref.test.ts b/__tests__/slugurlref.test.ts
index e502d3a..bc39abf 100644
--- a/__tests__/slugurlref.test.ts
+++ b/__tests__/slugurlref.test.ts
@@ -25,6 +25,11 @@ test('slug_url_ref: a fix branch', () => {
   test_slugurlref_cs('refs/heads/fix/issue_number', 'fix-issue-number')
 })
 
+test('slug_url_ref: an underscore', () => {
+  test_slugurlref('refs/heads/An_Underscore', 'an-underscore')
+  test_slugurlref_cs('refs/heads/An_Underscore', 'An-Underscore')
+})
+
 test('slug_url_ref: a simple tag', () => {
   test_slugurlref('refs/tags/v1.0.0', 'v1-0-0')
   test_slugurlref_cs('refs/tags/v1.0.0', 'v1-0-0')