diff --git a/includes/debug/DeprecationHelper.php b/includes/debug/DeprecationHelper.php
index 2e78535eac4..919dd2c5960 100644
--- a/includes/debug/DeprecationHelper.php
+++ b/includes/debug/DeprecationHelper.php
@@ -198,6 +198,12 @@ trait DeprecationHelper {
 		if ( $ownerClass ) {
 			// Someone tried to access a normal non-public property. Try to behave like PHP would.
 			trigger_error( "Cannot access non-public property $qualifiedName", E_USER_ERROR );
+		} elseif ( property_exists( $this, $name ) ) {
+			// Normally __get method will not be even called if the property exists,
+			// but in tests if we mock an object that uses DeprecationHelper,
+			// __get and __set magic methods will be mocked as well, and called
+			// regardless of the property existence. Support that use-case.
+			return $this->$name;
 		} else {
 			// Non-existing property. Try to behave like PHP would.
 			trigger_error( "Undefined property: $qualifiedName", E_USER_NOTICE );
diff --git a/tests/phpunit/includes/debug/DeprecationHelperTest.php b/tests/phpunit/includes/debug/DeprecationHelperTest.php
index b438247610f..565b04aa242 100644
--- a/tests/phpunit/includes/debug/DeprecationHelperTest.php
+++ b/tests/phpunit/includes/debug/DeprecationHelperTest.php
@@ -78,6 +78,14 @@ class DeprecationHelperTest extends MediaWikiIntegrationTestCase {
 		} );
 	}
 
+	public function testDynamicPropertyOnMockObject() {
+		$testObject = $this->getMockBuilder( TestDeprecatedClass::class )
+			->enableProxyingToOriginalMethods()
+			->getMock();
+		$testObject->blabla = 'test';
+		$this->assertSame( 'test', $testObject->blabla );
+	}
+
 	/**
 	 * @dataProvider provideSet
 	 */