diff --git a/src/lib/types.ts b/src/lib/types.ts
index 23cf4d5c..13083dd1 100644
--- a/src/lib/types.ts
+++ b/src/lib/types.ts
@@ -43,7 +43,7 @@ export interface Config {
      * A class group ID is the key of a class group in classGroups object.
      * @example { 'font-size': ['leading'] }
      */
-    conflictingClassGroupModifiers?: Record<ClassGroupId, readonly ClassGroupId[]>
+    conflictingClassGroupModifiers: Record<ClassGroupId, readonly ClassGroupId[]>
 }
 
 export type ThemeObject = Record<string, ClassGroup>
diff --git a/tests/create-tailwind-merge.test.ts b/tests/create-tailwind-merge.test.ts
index 594ec061..1c34716e 100644
--- a/tests/create-tailwind-merge.test.ts
+++ b/tests/create-tailwind-merge.test.ts
@@ -14,6 +14,7 @@ test('createTailwindMerge works with single config function', () => {
             fooKey: ['otherKey'],
             otherKey: ['fooKey', 'fooKey2'],
         },
+        conflictingClassGroupModifiers: {},
     }))
 
     expect(tailwindMerge('')).toBe('')
@@ -54,6 +55,7 @@ test('createTailwindMerge works with multiple config functions', () => {
                 fooKey: ['otherKey'],
                 otherKey: ['fooKey', 'fooKey2'],
             },
+            conflictingClassGroupModifiers: {},
         }),
         (config) => ({
             ...config,
diff --git a/tests/merge-configs.test.ts b/tests/merge-configs.test.ts
index b544a7b2..5430db07 100644
--- a/tests/merge-configs.test.ts
+++ b/tests/merge-configs.test.ts
@@ -14,6 +14,9 @@ test('mergeConfigs has correct behavior', () => {
                     bla: [{ bli: ['blub', 'blublub'] }],
                 },
                 conflictingClassGroups: {},
+                conflictingClassGroupModifiers: {
+                    hello: ['world'],
+                },
             },
             {
                 classGroups: {
@@ -25,6 +28,9 @@ test('mergeConfigs has correct behavior', () => {
                     fooKey: ['otherKey'],
                     otherKey: ['fooKey', 'fooKey2'],
                 },
+                conflictingClassGroupModifiers: {
+                    hello: ['world2'],
+                },
             },
         ),
     ).toEqual({
@@ -43,5 +49,8 @@ test('mergeConfigs has correct behavior', () => {
             fooKey: ['otherKey'],
             otherKey: ['fooKey', 'fooKey2'],
         },
+        conflictingClassGroupModifiers: {
+            hello: ['world', 'world2'],
+        },
     })
 })
diff --git a/tests/public-api.test.ts b/tests/public-api.test.ts
index 49253129..c9a8eaa9 100644
--- a/tests/public-api.test.ts
+++ b/tests/public-api.test.ts
@@ -88,6 +88,7 @@ test('createTailwindMerge() has correct inputs and outputs', () => {
             theme: {},
             classGroups: {},
             conflictingClassGroups: {},
+            conflictingClassGroupModifiers: {},
         })),
     ).toStrictEqual(expect.any(Function))
 
@@ -104,6 +105,7 @@ test('createTailwindMerge() has correct inputs and outputs', () => {
             fooKey: ['otherKey'],
             otherKey: ['fooKey', 'fooKey2'],
         },
+        conflictingClassGroupModifiers: {},
     }))
 
     expect(tailwindMerge).toStrictEqual(expect.any(Function))
@@ -165,6 +167,7 @@ test('mergeConfigs has correct inputs and outputs', () => {
                     bla: [{ bli: ['blub', 'blublub'] }],
                 },
                 conflictingClassGroups: {},
+                conflictingClassGroupModifiers: {},
             },
             {},
         ),