Index: src/serialbus/serialbus.pro
--- src/serialbus/serialbus.pro.orig
+++ src/serialbus/serialbus.pro
@@ -52,7 +52,7 @@ SOURCES += \
     qmodbuspdu.cpp \
     qmodbusdeviceidentification.cpp
 
-qtConfig(modbus-serialport) {
+!openbsd:qtConfig(modbus-serialport) {
     QT_FOR_PRIVATE += serialport
 
     PUBLIC_HEADERS += \