diff --git a/src/lib/default-config.ts b/src/lib/default-config.ts
index 6b2858f6..e8b357ff 100644
--- a/src/lib/default-config.ts
+++ b/src/lib/default-config.ts
@@ -92,6 +92,7 @@ export function getDefaultConfig() {
 
     return {
         cacheSize: 500,
+        separator: ':',
         theme: {
             colors: [isAny],
             spacing: [isLength],
diff --git a/src/lib/modifier-utils.ts b/src/lib/modifier-utils.ts
index dc7f62b6..2a807972 100644
--- a/src/lib/modifier-utils.ts
+++ b/src/lib/modifier-utils.ts
@@ -3,7 +3,7 @@ import { Config } from './types'
 export const IMPORTANT_MODIFIER = '!'
 
 export function createSplitModifiers(config: Config) {
-    const separator = config.separator || ':'
+    const separator = config.separator
     const isSeparatorSingleCharacter = separator.length === 1
     const firstSeparatorCharacter = separator[0]
     const separatorLength = separator.length
diff --git a/src/lib/types.ts b/src/lib/types.ts
index 7b3d4e72..23cf4d5c 100644
--- a/src/lib/types.ts
+++ b/src/lib/types.ts
@@ -14,7 +14,7 @@ export interface Config {
      * Custom separator for modifiers in Tailwind classes
      * @see https://tailwindcss.com/docs/configuration#separator
      */
-    separator?: string
+    separator: string
     /**
      * Theme scales used in classGroups.
      * The keys are the same as in the Tailwind config but the values are sometimes defined more broadly.
diff --git a/tests/create-tailwind-merge.test.ts b/tests/create-tailwind-merge.test.ts
index 3007de07..594ec061 100644
--- a/tests/create-tailwind-merge.test.ts
+++ b/tests/create-tailwind-merge.test.ts
@@ -3,6 +3,7 @@ import { createTailwindMerge } from '../src'
 test('createTailwindMerge works with single config function', () => {
     const tailwindMerge = createTailwindMerge(() => ({
         cacheSize: 20,
+        separator: ':',
         theme: {},
         classGroups: {
             fooKey: [{ fooKey: ['bar', 'baz'] }],
@@ -42,6 +43,7 @@ test('createTailwindMerge works with multiple config functions', () => {
     const tailwindMerge = createTailwindMerge(
         () => ({
             cacheSize: 20,
+            separator: ':',
             theme: {},
             classGroups: {
                 fooKey: [{ fooKey: ['bar', 'baz'] }],
diff --git a/tests/merge-configs.test.ts b/tests/merge-configs.test.ts
index 36c02074..b544a7b2 100644
--- a/tests/merge-configs.test.ts
+++ b/tests/merge-configs.test.ts
@@ -5,6 +5,7 @@ test('mergeConfigs has correct behavior', () => {
         mergeConfigs(
             {
                 cacheSize: 50,
+                separator: ':',
                 theme: {
                     hi: ['ho'],
                 },
@@ -28,6 +29,7 @@ test('mergeConfigs has correct behavior', () => {
         ),
     ).toEqual({
         cacheSize: 50,
+        separator: ':',
         theme: {
             hi: ['ho'],
         },
diff --git a/tests/modifiers.test.ts b/tests/modifiers.test.ts
index 6088f2c5..18152566 100644
--- a/tests/modifiers.test.ts
+++ b/tests/modifiers.test.ts
@@ -17,6 +17,7 @@ test('conflicts across postfix modifiers', () => {
 
     const customTwMerge = createTailwindMerge(() => ({
         cacheSize: 10,
+        separator: ':',
         theme: {},
         classGroups: {
             foo: ['foo-1/2', 'foo-2/3'],
diff --git a/tests/public-api.test.ts b/tests/public-api.test.ts
index 61d2b689..49253129 100644
--- a/tests/public-api.test.ts
+++ b/tests/public-api.test.ts
@@ -84,6 +84,7 @@ test('createTailwindMerge() has correct inputs and outputs', () => {
     expect(
         createTailwindMerge(() => ({
             cacheSize: 0,
+            separator: ':',
             theme: {},
             classGroups: {},
             conflictingClassGroups: {},
@@ -92,6 +93,7 @@ test('createTailwindMerge() has correct inputs and outputs', () => {
 
     const tailwindMerge = createTailwindMerge(() => ({
         cacheSize: 20,
+        separator: ':',
         theme: {},
         classGroups: {
             fooKey: [{ fooKey: ['bar', 'baz'] }],
@@ -156,6 +158,7 @@ test('mergeConfigs has correct inputs and outputs', () => {
         mergeConfigs(
             {
                 cacheSize: 50,
+                separator: ':',
                 theme: {},
                 classGroups: {
                     fooKey: [{ fooKey: ['one', 'two'] }],