diff --git a/src/internal/__tests__/validate-string.spec-d.ts b/src/internal/__tests__/validate-string.spec-d.ts
new file mode 100644
index 00000000..1050ec09
--- /dev/null
+++ b/src/internal/__tests__/validate-string.spec-d.ts
@@ -0,0 +1,12 @@
+/**
+ * @file Type Tests - validateString
+ * @module pathe/internal/tests/unit-d/validateString
+ */
+
+import testSubject from '../validate-string'
+
+describe('unit-d:internal/validateString', () => {
+  it('should extract string guard value', () => {
+    expectTypeOf(testSubject).guards.toBeString()
+  })
+})
diff --git a/src/internal/__tests__/validate-string.spec.ts b/src/internal/__tests__/validate-string.spec.ts
new file mode 100644
index 00000000..ff04ddcc
--- /dev/null
+++ b/src/internal/__tests__/validate-string.spec.ts
@@ -0,0 +1,34 @@
+/**
+ * @file Unit Tests - validateString
+ * @module pathe/internal/tests/unit/validateString
+ */
+
+import ERR_INVALID_ARG_TYPE from '../err-invalid-arg-type'
+import testSubject from '../validate-string'
+
+describe('unit:internal/validateString', () => {
+  let name: string
+
+  beforeEach(() => {
+    name = 'path'
+  })
+
+  it('should return true if value is typeof string', () => {
+    expect(testSubject(faker.datatype.string(13), name)).to.be.true
+  })
+
+  it('should throw if value is not typeof string', () => {
+    // Arrange
+    let error: ERR_INVALID_ARG_TYPE
+
+    // Act
+    try {
+      testSubject(null, name)
+    } catch (e: unknown) {
+      error = e as typeof error
+    }
+
+    // Expect
+    expect(error!).to.be.instanceOf(ERR_INVALID_ARG_TYPE)
+  })
+})
diff --git a/src/internal/validate-string.ts b/src/internal/validate-string.ts
new file mode 100644
index 00000000..191baadb
--- /dev/null
+++ b/src/internal/validate-string.ts
@@ -0,0 +1,25 @@
+/**
+ * @file Internal - validateString
+ * @module pathe/internal/validateString
+ */
+
+import ERR_INVALID_ARG_TYPE from './err-invalid-arg-type'
+
+/**
+ * Checks if `value` is a string.
+ *
+ * Throws {@linkcode ERR_INVALID_ARG_TYPE} if `value` is not a string.
+ *
+ * [1]: https://nodejs.org/api/errors.html#err_invalid_arg_type
+ *
+ * @param {unknown} value - Possible string value
+ * @param {string} name - `value` label
+ * @return {boolean} `true` if `value` is a string
+ * @throws {ERR_INVALID_ARG_TYPE}
+ */
+const validateString = (value: unknown, name: string): value is string => {
+  if (typeof value === 'string') return true
+  throw new ERR_INVALID_ARG_TYPE(name, 'string', value)
+}
+
+export default validateString