diff --git a/packages/quill/src/core/quill.ts b/packages/quill/src/core/quill.ts
index 5622856527..135a7b73a2 100644
--- a/packages/quill/src/core/quill.ts
+++ b/packages/quill/src/core/quill.ts
@@ -30,18 +30,7 @@ const debug = logger('quill');
 const globalRegistry = new Parchment.Registry();
 Parchment.ParentBlot.uiClass = 'ql-ui';
 
-type ClassToConstructor<T> = { new (...args: any[]): T & object };
-
-type RegistryTarget = Parchment.RegistryDefinition | Module | boolean;
-
-interface RegistryRecord {
-  [key: `blots/${string}`]: Parchment.BlotConstructor;
-  [key: `formats/${string}`]: Parchment.RegistryDefinition;
-  [key: `attributors/${string}`]: Parchment.Attributor;
-  [key: `modules/${string}`]: ClassToConstructor<Module>;
-  [key: `themes/${string}`]: ClassToConstructor<Theme>;
-  [key: string]: any;
-}
+type RegisterTarget = Parchment.RegistryDefinition | Theme | Module | Function; // ES5 constructor functions
 
 /**
  * Options for initializing a Quill instance
@@ -134,21 +123,39 @@ class Quill {
     return this.imports[name];
   }
 
-  static register(record: RegistryRecord, overwrite?: boolean): void;
   static register(
-    target: Exclude<RegistryTarget, boolean | Module>,
+    targets: Record<string, RegisterTarget>,
+    overwrite?: boolean,
+  ): void;
+  static register(
+    target: Parchment.RegistryDefinition,
     overwrite?: boolean,
   ): void;
   static register(
     path: string,
-    target: RegistryTarget,
+    target: RegisterTarget,
     overwrite?: boolean,
   ): void;
   static register(...args: any[]): void {
-    const path = typeof args[0] === 'string' ? args[0] : '';
-    const target = path ? args[1] : args[0];
-    const overwrite = (path ? args[2] : args[1]) ?? false;
-    if (path) {
+    if (typeof args[0] !== 'string') {
+      const target = args[0];
+      const overwrite = !!args[1];
+
+      const name = 'attrName' in target ? target.attrName : target.blotName;
+      if (typeof name === 'string') {
+        // Shortcut for formats:
+        // register(Blot | Attributor, overwrite)
+        this.register(`formats/${name}`, target, overwrite);
+      } else {
+        Object.keys(target).forEach((key) => {
+          this.register(key, target[key], overwrite);
+        });
+      }
+    } else {
+      const path = args[0];
+      const target = args[1];
+      const overwrite = !!args[2];
+
       if (this.imports[path] != null && !overwrite) {
         debug.warn(`Overwriting ${path} with`, target);
       }
@@ -164,16 +171,6 @@ class Quill {
       if (typeof target.register === 'function') {
         target.register(globalRegistry);
       }
-      return;
-    }
-    const name: string | undefined = target['attrName'] ?? target['blotName'];
-    if (typeof name === 'string') {
-      // register(Blot | Attributor, overwrite)
-      this.register(`formats/${name}`, target, overwrite);
-    } else {
-      Object.keys(target).forEach((key) => {
-        this.register(key, target[key], overwrite);
-      });
     }
   }
 
diff --git a/packages/quill/src/modules/syntax.ts b/packages/quill/src/modules/syntax.ts
index c3d1a81959..da99fdc41d 100644
--- a/packages/quill/src/modules/syntax.ts
+++ b/packages/quill/src/modules/syntax.ts
@@ -80,7 +80,6 @@ class SyntaxCodeBlock extends CodeBlock {
     }
   }
 
-  // TODO maybe something wrong
   replaceWith(name: string | Blot, value?: any) {
     this.formatAt(0, this.length(), CodeToken.blotName, false);
     return super.replaceWith(name, value);
diff --git a/packages/quill/src/quill.ts b/packages/quill/src/quill.ts
index de2f0a609f..648183434b 100644
--- a/packages/quill/src/quill.ts
+++ b/packages/quill/src/quill.ts
@@ -115,7 +115,7 @@ Quill.register(
   true,
 );
 
-export { default as Module } from './core/module.js';
+export { Module } from './core.js';
 export type {
   Bounds,
   DebugLevel,
diff --git a/packages/quill/test/types/quill.test-d.ts b/packages/quill/test/types/quill.test-d.ts
index 1d65de3823..cb3873ea06 100644
--- a/packages/quill/test/types/quill.test-d.ts
+++ b/packages/quill/test/types/quill.test-d.ts
@@ -3,6 +3,37 @@ import Quill from '../../src/quill.js';
 import type { EmitterSource, Parchment, Range } from '../../src/quill.js';
 import Delta from 'quill-delta';
 import type { default as Block, BlockEmbed } from '../../src/blots/block.js';
+import SnowTheme from '../../src/themes/snow.js';
+import { LeafBlot } from 'parchment';
+
+{
+  const Counter = (quill: Quill, options: { unit: string }) => {
+    console.log(quill, options);
+  };
+  Quill.register('modules/counter', Counter);
+  Quill.register('themes/snow', SnowTheme);
+  Quill.register('themes/snow', SnowTheme, true);
+
+  class MyBlot extends LeafBlot {}
+
+  Quill.register(MyBlot);
+  Quill.register(MyBlot, true);
+  // @ts-expect-error
+  Quill.register(SnowTheme);
+  Quill.register({
+    'modules/counter': Counter,
+    'themes/snow': SnowTheme,
+    'formats/my-blot': MyBlot,
+  });
+  Quill.register(
+    {
+      'modules/counter': Counter,
+      'themes/snow': SnowTheme,
+      'formats/my-blot': MyBlot,
+    },
+    true,
+  );
+}
 
 const quill = new Quill('#editor');
 
diff --git a/packages/quill/test/unit/core/quill.spec.ts b/packages/quill/test/unit/core/quill.spec.ts
index ca9f413afc..0df2b40a98 100644
--- a/packages/quill/test/unit/core/quill.spec.ts
+++ b/packages/quill/test/unit/core/quill.spec.ts
@@ -1,7 +1,7 @@
 import '../../../src/quill.js';
 import Delta from 'quill-delta';
-import { Registry } from 'parchment';
-import { beforeEach, describe, expect, test, vitest } from 'vitest';
+import { LeafBlot, Registry } from 'parchment';
+import { afterEach, beforeEach, describe, expect, test, vitest } from 'vitest';
 import type { MockedFunction } from 'vitest';
 import Emitter from '../../../src/core/emitter.js';
 import Theme from '../../../src/core/theme.js';
@@ -29,6 +29,47 @@ describe('Quill', () => {
     });
   });
 
+  describe('register', () => {
+    const imports = { ...Quill.imports };
+    afterEach(() => {
+      Quill.imports = imports;
+    });
+
+    test('register(path, target)', () => {
+      class Counter {}
+      Quill.register('modules/counter', Counter);
+
+      expect(Quill.imports).toHaveProperty('modules/counter', Counter);
+      expect(Quill.import('modules/counter')).toEqual(Counter);
+    });
+
+    test('register(formats)', () => {
+      class MyCounterBlot extends LeafBlot {
+        static blotName = 'my-counter';
+        static className = 'ql-my-counter';
+      }
+      Quill.register(MyCounterBlot);
+
+      expect(Quill.imports).toHaveProperty('formats/my-counter', MyCounterBlot);
+      expect(Quill.import('formats/my-counter')).toEqual(MyCounterBlot);
+    });
+
+    test('register(targets)', () => {
+      class ABlot extends LeafBlot {
+        static blotName = 'a-blot';
+        static className = 'ql-a-blot';
+      }
+      class AModule {}
+      Quill.register({
+        'formats/a-blot': ABlot,
+        'modules/a-module': AModule,
+      });
+
+      expect(Quill.import('formats/a-blot')).toEqual(ABlot);
+      expect(Quill.import('modules/a-module')).toEqual(AModule);
+    });
+  });
+
   describe('construction', () => {
     test('empty', () => {
       const quill = new Quill(createContainer());