diff --git a/src/Generator/AnonClassGenerator.php b/src/Generator/AnonClassGenerator.php
index 6152bc86..c98eb024 100644
--- a/src/Generator/AnonClassGenerator.php
+++ b/src/Generator/AnonClassGenerator.php
@@ -177,6 +177,14 @@ trait AnonClassGenerator
                         $class = $this->classStack[count($this->classStack) - 1] ?? null;
                         if ($class !== null && $this->compiler->shouldAddMixedReturnToEmbeddedClassMethod($class, $node)) {
                             $node->returnType = new Identifier('mixed');
+                            // An implicit fallthrough returns null in PHP. Once the
+                            // compatibility return type is made explicit, PHP requires
+                            // an explicit value on that path as well.
+                            if ($node->stmts !== null) {
+                                $node->stmts[] = new Node\Stmt\Return_(
+                                    new Node\Expr\ConstFetch(new Name('null')),
+                                );
+                            }
                         }
                     }
                     return null;
diff --git a/tests/compiler/anon_class/005.phpt b/tests/compiler/anon_class/005.phpt
index c3650797..c44495d4 100644
--- a/tests/compiler/anon_class/005.phpt
+++ b/tests/compiler/anon_class/005.phpt
@@ -14,16 +14,23 @@ namespace AnonymousClassSupport {
     function accepts(Subject $value): bool {
         return true;
     }
+
+    class Visitor {
+        public function inspect(object $value) {
+            return null;
+        }
+    }
 }
 
 namespace AnonymousClassConsumer {
     use AnonymousClassSupport\Marker as ImportedMarker;
     use AnonymousClassSupport\Subject as ImportedSubject;
+    use AnonymousClassSupport\Visitor as ImportedVisitor;
     use const AnonymousClassSupport\FLAG as IMPORTED_FLAG;
     use function AnonymousClassSupport\accepts as imported_accepts;
 
     function main(): void {
-        $visitor = new class('ready') {
+        $visitor = new class('ready') extends ImportedVisitor {
             public function __construct(private readonly string $state) {}
 
             public function accepts(object $value): bool {
@@ -33,9 +40,16 @@ namespace AnonymousClassConsumer {
                     && imported_accepts($value)
                     && $this->state === 'ready';
             }
+
+            public function inspect(object $value) {
+                if ($value instanceof ImportedSubject) {
+                    return 'subject';
+                }
+            }
         };
 
         var_dump($visitor->accepts(new ImportedSubject()));
+        var_dump($visitor->inspect(new \stdClass()));
     }
 }
 
@@ -47,3 +61,4 @@ namespace {
 ?>
 --EXPECT--
 bool(true)
+NULL