diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2fe45169a2..709c47d0b1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@
 
 - Include source maps for Parchment
 - **Clipboard** Support pasting links copied from iOS share sheets
+- Fix config parsing where undefined values were kept
 
 # 2.0.0-rc.3
 
diff --git a/packages/quill/src/core/quill.ts b/packages/quill/src/core/quill.ts
index 148933a4ee..ab900c5785 100644
--- a/packages/quill/src/core/quill.ts
+++ b/packages/quill/src/core/quill.ts
@@ -747,6 +747,12 @@ function expandModuleConfig(config: Record<string, unknown> | undefined) {
   );
 }
 
+function omitUndefinedValuesFromOptions(obj: Options) {
+  return Object.fromEntries(
+    Object.entries(obj).filter((entry) => entry[1] !== undefined),
+  );
+}
+
 function expandConfig(
   containerOrSelector: HTMLElement | string,
   options: Options,
@@ -785,7 +791,11 @@ function expandConfig(
     };
   }
 
-  const config = { ...quillDefaults, ...themeDefaults, ...options };
+  const config = {
+    ...quillDefaults,
+    ...omitUndefinedValuesFromOptions(themeDefaults),
+    ...omitUndefinedValuesFromOptions(options),
+  };
 
   let registry = options.registry;
   if (registry) {
diff --git a/packages/quill/test/unit/core/quill.spec.ts b/packages/quill/test/unit/core/quill.spec.ts
index 9680b200a8..dc17087b96 100644
--- a/packages/quill/test/unit/core/quill.spec.ts
+++ b/packages/quill/test/unit/core/quill.spec.ts
@@ -790,6 +790,13 @@ describe('Quill', () => {
       expect(config.registry).toBe(globalRegistry);
     });
 
+    test('registry with undefined values', () => {
+      const config = expandConfig(`#${testContainerId}`, {
+        registry: undefined,
+      });
+      expect(config.registry).toBe(globalRegistry);
+    });
+
     describe('formats', () => {
       test('null value allows all formats', () => {
         const config = expandConfig(`#${testContainerId}`, {
@@ -800,6 +807,15 @@ describe('Quill', () => {
         expect(config.registry.query('bold')).toBeTruthy();
       });
 
+      test('undefined value allows all formats', () => {
+        const config = expandConfig(`#${testContainerId}`, {
+          formats: undefined,
+        });
+
+        expect(config.registry.query('cursor')).toBeTruthy();
+        expect(config.registry.query('bold')).toBeTruthy();
+      });
+
       test('always allows core formats', () => {
         const config = expandConfig(`#${testContainerId}`, {
           formats: ['bold'],