diff --git a/xs/t/15_config.t b/xs/t/15_config.t
index 8981e0095..a79fe7a37 100644
--- a/xs/t/15_config.t
+++ b/xs/t/15_config.t
@@ -70,7 +70,7 @@ foreach my $config (Slic3r::Config->new, Slic3r::Config::Static::new_FullPrintCo
     ok abs($config->get('first_layer_height') - 0.3) < 1e-4, 'set/get absolute floatOrPercent';
     is $config->opt_serialize('first_layer_height'), '0.3', 'serialize absolute floatOrPercent';
     
-    $config->set('first_layer_height', $config->layer_height);
+    $config->set('first_layer_height', $config->get('layer_height'));
     $config->get_abs_value('first_layer_height');
     ok abs($config->get_abs_value('first_layer_height') - 0.15) < 1e-4, 'set/get relative floatOrPercent';
 #    is $config->opt_serialize('first_layer_height'), '50%', 'serialize relative floatOrPercent';