diff --git a/src/Controller/PartController.php b/src/Controller/PartController.php
index 6b9472fd..ee07f09f 100644
--- a/src/Controller/PartController.php
+++ b/src/Controller/PartController.php
@@ -234,7 +234,7 @@ final class PartController extends AbstractController
         } elseif ($assembly instanceof Assembly) {
             //Initialize a new part for a build part from the given assembly
             //Ensure that the assembly has not already a build part
-            if ($project->getBuildPart() instanceof Part) {
+            if ($assembly->getBuildPart() instanceof Part) {
                 $this->addFlash('error', 'part.new_build_part.error.build_part_already_exists');
                 return $this->redirectToRoute('part_edit', ['id' => $project->getBuildPart()->getID()]);
             }