diff --git a/src/utils.ts b/src/utils.ts
index 7b65a7ec78..e70a673e1c 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -72,6 +72,25 @@ export function mergeGlobalProperties(
 export const isObject = (obj: unknown): obj is Record<string, any> =>
   !!obj && typeof obj === 'object'
 
+function isClass(obj: unknown) {
+  if (!(obj instanceof Object)) return
+
+  const isCtorClass =
+    obj.constructor && obj.constructor.toString().substring(0, 5) === 'class'
+
+  if (!('prototype' in obj)) {
+    return isCtorClass
+  }
+
+  const prototype = obj.prototype as any
+  const isPrototypeCtorClass =
+    prototype.constructor &&
+    prototype.constructor.toString &&
+    prototype.constructor.toString().substring(0, 5) === 'class'
+
+  return isCtorClass || isPrototypeCtorClass
+}
+
 // https://stackoverflow.com/a/48218209
 export const mergeDeep = (
   target: Record<string, unknown>,
@@ -80,8 +99,13 @@ export const mergeDeep = (
   if (!isObject(target) || !isObject(source)) {
     return source
   }
+
   Object.keys(source)
-    .concat(Object.getOwnPropertyNames(Object.getPrototypeOf(source) ?? {}))
+    .concat(
+      isClass(source)
+        ? Object.getOwnPropertyNames(Object.getPrototypeOf(source) ?? {})
+        : Object.getOwnPropertyNames(source)
+    )
     .forEach((key) => {
       const targetValue = target[key]
       const sourceValue = source[key]
diff --git a/tests/utils.spec.ts b/tests/utils.spec.ts
new file mode 100644
index 0000000000..7678ce79f1
--- /dev/null
+++ b/tests/utils.spec.ts
@@ -0,0 +1,105 @@
+/**
+ * @vitest-environment node
+ */
+
+import { describe, expect, it } from 'vitest'
+import { mergeDeep } from '../src/utils'
+
+describe('utils', () => {
+  it('should be possible to replace a primitive value with another', () => {
+    // ARRANGE
+    const state = {
+      foo: 'bar'
+    }
+
+    // ACT
+    const result = mergeDeep(state, {
+      foo: true
+    })
+
+    // ASSERT
+    expect(result).toStrictEqual({
+      foo: true
+    })
+  })
+
+  it('should be possible to merge a nested object', () => {
+    // ARRANGE
+    const state = {
+      foo: {
+        bar: 'baz'
+      }
+    }
+
+    // ACT
+    const result = mergeDeep(state, {
+      foo: {
+        bar: 'bar',
+        foo: 'foo'
+      }
+    })
+
+    // ASSERT
+    expect(result).toStrictEqual({
+      foo: {
+        bar: 'bar',
+        foo: 'foo'
+      }
+    })
+  })
+
+  it('should be possible to replace an array', () => {
+    // ARRANGE
+    const state = {
+      foo: []
+    }
+
+    // ACT
+    const result = mergeDeep(state, {
+      foo: ['bar', 'baz']
+    })
+
+    // ASSERT
+    expect(result).toStrictEqual({
+      foo: ['bar', 'baz']
+    })
+  })
+
+  it('should be possible to add additional key', () => {
+    // ARRANGE
+    const state = {
+      foo: 'bar'
+    }
+
+    // ACT
+    const result = mergeDeep(state, {
+      baz: 'foo'
+    })
+
+    // ASSERT
+    expect(result).toStrictEqual({
+      foo: 'bar',
+      baz: 'foo'
+    })
+  })
+
+  it('should result in the same value as before merging', () => {
+    // ARRANGE
+    const state = {
+      foo: [],
+      bar: []
+    }
+
+    // ACT
+    const result = mergeDeep(state, {
+      foo: [],
+      bar: []
+    })
+
+    // ASSERT
+    expect(result).toStrictEqual({
+      foo: [],
+      bar: []
+    })
+  })
+})