diff --git a/ChangeLog-10.0.md b/ChangeLog-10.0.md
index 03d992ba3a4..23ab265c6b2 100644
--- a/ChangeLog-10.0.md
+++ b/ChangeLog-10.0.md
@@ -36,6 +36,7 @@ All notable changes of the PHPUnit 10.0 release series are documented in this fi
 * The JUnit XML logfile now has both `name` and `file` attributes on `<testcase>` elements for PHPT tests
 * The `forceCoversAnnotation` attribute of the `<phpunit>` element of PHPUnit's XML configuration file has been renamed to `requireCoverageMetadata`
 * The `beStrictAboutCoversAnnotation` attribute of the `<phpunit>` element of PHPUnit's XML configuration file has been renamed to `beStrictAboutCoverageMetadata`
+* [#4852](https://github.com/sebastianbergmann/phpunit/issues/4852): Allow using `addMethods` when `allowMockingUnknownTypes` is true in MockBuilder
 
 ### Removed
 
diff --git a/src/Framework/MockObject/MockBuilder.php b/src/Framework/MockObject/MockBuilder.php
index dbd907f3969..ae26c96b258 100644
--- a/src/Framework/MockObject/MockBuilder.php
+++ b/src/Framework/MockObject/MockBuilder.php
@@ -212,21 +212,23 @@ public function addMethods(array $methods): self
             return $this;
         }
 
-        try {
-            $reflector = new ReflectionClass($this->type);
-            // @codeCoverageIgnoreStart
-        } catch (\ReflectionException $e) {
-            throw new ReflectionException(
-                $e->getMessage(),
-                (int) $e->getCode(),
-                $e
-            );
-        }
-        // @codeCoverageIgnoreEnd
+        if (!$this->allowMockingUnknownTypes) {
+            try {
+                $reflector = new ReflectionClass($this->type);
+                // @codeCoverageIgnoreStart
+            } catch (\ReflectionException $e) {
+                throw new ReflectionException(
+                    $e->getMessage(),
+                    (int) $e->getCode(),
+                    $e
+                );
+            }
+            // @codeCoverageIgnoreEnd
 
-        foreach ($methods as $method) {
-            if ($reflector->hasMethod($method)) {
-                throw new CannotUseAddMethodsException($this->type, $method);
+            foreach ($methods as $method) {
+                if ($reflector->hasMethod($method)) {
+                    throw new CannotUseAddMethodsException($this->type, $method);
+                }
             }
         }
 
diff --git a/tests/unit/Framework/MockObject/MockBuilderTest.php b/tests/unit/Framework/MockObject/MockBuilderTest.php
index 10ef2a11d80..865f1038fc9 100644
--- a/tests/unit/Framework/MockObject/MockBuilderTest.php
+++ b/tests/unit/Framework/MockObject/MockBuilderTest.php
@@ -123,6 +123,27 @@ public function testAbleToUseOnlyMethodsAfterAddMethods(): void
         $this->assertNull($mock->mockableMethod());
     }
 
+    public function testAddMethodsWithNonExistingClassName(): void
+    {
+        $this->expectException(\PHPUnit\Framework\MockObject\ReflectionException::class);
+        $this->expectErrorMessage('Class "FooBar" does not exist');
+
+        $this->getMockBuilder('FooBar')
+            ->disallowMockingUnknownTypes()
+            ->addMethods(['mockableMethod'])
+            ->getMock();
+    }
+
+    public function testAddMethodsWithNonExistingClassNameAndAllowMockingUnknownTypes(): void
+    {
+        $mock = $this->getMockBuilder('FooBar')
+            ->allowMockingUnknownTypes()
+            ->addMethods(['mockableMethod'])
+            ->getMock();
+
+        $this->assertNull($mock->mockableMethod());
+    }
+
     public function testByDefaultDoesNotPassArgumentsToTheConstructor(): void
     {
         $mock = $this->getMockBuilder(Mockable::class)->getMock();