diff --git a/t/perimeters.t b/t/perimeters.t
index 513c76ef98..7b66183898 100644
--- a/t/perimeters.t
+++ b/t/perimeters.t
@@ -318,6 +318,7 @@ use Slic3r::Test;
     $config->set('nozzle_diameter', [0.4]);
     $config->set('perimeters', 2);
     $config->set('perimeter_extrusion_width', 0.4);
+    $config->set('external_perimeter_extrusion_width', 0.4);
     $config->set('infill_extrusion_width', 0.53);
     $config->set('solid_infill_extrusion_width', 0.53);