diff --git a/xs/src/slic3r/GUI/Field.cpp b/xs/src/slic3r/GUI/Field.cpp
index 54cd080b4..56d3d55d5 100644
--- a/xs/src/slic3r/GUI/Field.cpp
+++ b/xs/src/slic3r/GUI/Field.cpp
@@ -220,8 +220,8 @@ void SpinCtrl::BUILD() {
 // 		# gets the old one, and on_kill_focus resets the control to the old value.
 // 		# As a workaround, we get the new value from $event->GetString and store
 // 		# here temporarily so that we can return it from $self->get_value
-		std::string value = e.GetString();
-		if (is_matched(value, "^\d+$"))
+		std::string value = e.GetString().utf8_str();
+		if (is_matched(value, "^\\d+$"))
 			tmp_value = std::stoi(value);
 		on_change_field(e);
 // 		# We don't reset tmp_value here because _on_change might put callbacks