diff --git a/src/internal/__tests__/is-sep.spec-d.ts b/src/internal/__tests__/is-sep.spec-d.ts
new file mode 100644
index 00000000..a05490bb
--- /dev/null
+++ b/src/internal/__tests__/is-sep.spec-d.ts
@@ -0,0 +1,13 @@
+/**
+ * @file Type Tests - isSep
+ * @module pathe/internal/tests/unit-d/isSep
+ */
+
+import type { Sep } from '#src/types'
+import testSubject from '../is-sep'
+
+describe('unit-d:internal/isSep', () => {
+  it('should guard Sep', () => {
+    expectTypeOf(testSubject).guards.toEqualTypeOf<Sep>()
+  })
+})
diff --git a/src/internal/__tests__/is-sep.spec.ts b/src/internal/__tests__/is-sep.spec.ts
new file mode 100644
index 00000000..1d03c863
--- /dev/null
+++ b/src/internal/__tests__/is-sep.spec.ts
@@ -0,0 +1,17 @@
+/**
+ * @file Unit Tests - isSep
+ * @module pathe/internal/tests/unit/isSep
+ */
+
+import { posix, win32 } from 'node:path'
+import testSubject from '../is-sep'
+
+describe('unit:internal/isSep', () => {
+  it('should return false if value is not path separator', () => {
+    expect(testSubject(win32.sep)).to.be.false
+  })
+
+  it('should return true if value is path separator', () => {
+    expect(testSubject(posix.sep)).to.be.true
+  })
+})
diff --git a/src/internal/is-sep.ts b/src/internal/is-sep.ts
new file mode 100644
index 00000000..fd91977e
--- /dev/null
+++ b/src/internal/is-sep.ts
@@ -0,0 +1,21 @@
+/**
+ * @file Internal - isSep
+ * @module pathe/internal/isSep
+ */
+
+import sep from '#src/lib/sep'
+import type { Sep } from '#src/types'
+
+/**
+ * Checks if `value` is a path separator.
+ *
+ * [1]: {@link ../lib/sep.ts}
+ *
+ * @see [`sep`][1]
+ *
+ * @param {unknown} value - Possible path separator
+ * @return {value is Sep} `true` if `str` is path separator
+ */
+const isSep = (value: unknown): value is Sep => value === sep
+
+export default isSep
diff --git a/src/lib/basename.ts b/src/lib/basename.ts
index a948840c..858d19ab 100644
--- a/src/lib/basename.ts
+++ b/src/lib/basename.ts
@@ -5,8 +5,8 @@
 
 import ensurePosix from '#src/internal/ensure-posix'
 import isDrivePath from '#src/internal/is-drive-path'
+import isSep from '#src/internal/is-sep'
 import validateString from '#src/internal/validate-string'
-import sep from './sep'
 
 /**
  * Returns the last portion of a path, similar to the Unix `basename` command.
@@ -55,7 +55,7 @@ const basename = (path: string, suffix?: string): string => {
   // get basename without attempting to remove suffix
   if (!suffix || suffix.length > path.length) {
     for (let i = path.length - 1; i >= start; --i) {
-      if (path.charAt(i) === sep) {
+      if (isSep(path.charAt(i))) {
         // if separator was reached, and is not a trailing separator, exit early
         if (!sep_match) {
           start = i + 1
@@ -94,7 +94,7 @@ const basename = (path: string, suffix?: string): string => {
      */
     const char: string = path.charAt(i)
 
-    if (char === sep) {
+    if (isSep(char)) {
       // if separator was reached, and is not a trailing separator, exit early
       if (!sep_match) {
         start = i + 1