diff --git a/src/AspectWeaver.php b/src/AspectWeaver.php
index 8939039..9b3b112 100644
--- a/src/AspectWeaver.php
+++ b/src/AspectWeaver.php
@@ -399,7 +399,10 @@ class AspectWeaver
         if ($type instanceof ReflectionNamedType) {
             $name = $type->getName();
 
-            // Don't add ? for nullable built-in types that already allow null
+            if (!$type->isBuiltin()) {
+                $name = '\\' . $name;
+            }
+
             if ($type->allowsNull() && $name !== 'mixed' && $name !== 'null') {
                 return '?' . $name;
             }
diff --git a/tests/Classes/CallsImportedClass.php b/tests/Classes/CallsImportedClass.php
new file mode 100644
index 0000000..81631a6
--- /dev/null
+++ b/tests/Classes/CallsImportedClass.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace Tests\Classes;
+
+use Tests\Aspects\BasicAspect;
+use Tests\Classes\Internal\ImportedClass;
+
+class CallsImportedClass
+{
+    #[BasicAspect]
+    public function dependsOnOther(ImportedClass $object, object $sideEffect): ImportedClass
+    {
+        return $object;
+    }
+}
diff --git a/tests/Classes/Internal/ImportedClass.php b/tests/Classes/Internal/ImportedClass.php
new file mode 100644
index 0000000..61d7e83
--- /dev/null
+++ b/tests/Classes/Internal/ImportedClass.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Tests\Classes\Internal;
+
+class ImportedClass
+{
+    public readonly string $data;
+}
diff --git a/tests/ImportedClassTest.php b/tests/ImportedClassTest.php
new file mode 100644
index 0000000..e8d3d2e
--- /dev/null
+++ b/tests/ImportedClassTest.php
@@ -0,0 +1,20 @@
+<?php
+
+use PHPUnit\Framework\TestCase;
+use Tests\Classes\CallsImportedClass;
+use Tests\Classes\Internal\ImportedClass;
+
+final class ImportedClassTest extends TestCase
+{
+    public function testAspectMethodIsCalled(): void
+    {
+        $c = new CallsImportedClass();
+
+        $o = new ImportedClass();
+
+        $sideEffect = (object) ['before' => false, 'after' => false];
+        $c->dependsOnOther($o, $sideEffect);
+        $this->assertTrue($sideEffect->before);
+        $this->assertTrue($sideEffect->after);
+    }
+}
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index aed571a..cb424f9 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -9,6 +9,7 @@ use Tests\Aspects\TrackingAspect;
 use Tests\Aspects\ThrowingAspect;
 use Tests\Aspects\ModifyingAspect;
 use Tests\Aspects\ConfigurableAspect;
+use Tests\Classes\CallsImportedClass;
 use Tests\Classes\WrappedClass;
 use Tests\Classes\ParameterTypesClass;
 use Tests\Classes\StackedAspectsClass;
@@ -34,6 +35,7 @@ $loader = AspectBuilder::begin()
         ThrowingClass::class,
         ModifyingClass::class,
         ConfigurableClass::class,
+        CallsImportedClass::class,
     ])
     ->build($weaver)
     ->register();