diff --git a/utils/GPSsmooth/MIDG_main.cxx b/utils/GPSsmooth/MIDG_main.cxx
index 7b8141254..118c6198b 100644
--- a/utils/GPSsmooth/MIDG_main.cxx
+++ b/utils/GPSsmooth/MIDG_main.cxx
@@ -4,6 +4,8 @@
 
 #ifdef HAVE_WINDOWS_H
 #  include <windows.h>
+#else
+#  include <netinet/in.h>       // htonl() ntohl()
 #endif
 
 #include <iostream>
diff --git a/utils/GPSsmooth/UGear_main.cxx b/utils/GPSsmooth/UGear_main.cxx
index faf5d725f..43d44b6f2 100644
--- a/utils/GPSsmooth/UGear_main.cxx
+++ b/utils/GPSsmooth/UGear_main.cxx
@@ -4,6 +4,8 @@
 
 #ifdef HAVE_WINDOWS_H
 #  include <windows.h>
+#else
+#  include <netinet/in.h>       // htonl() ntohl()
 #endif
 
 #ifndef _WIN32
diff --git a/utils/GPSsmooth/gps_main.cxx b/utils/GPSsmooth/gps_main.cxx
index 1b98b04a3..5dfc76c67 100644
--- a/utils/GPSsmooth/gps_main.cxx
+++ b/utils/GPSsmooth/gps_main.cxx
@@ -4,6 +4,8 @@
 
 #ifdef HAVE_WINDOWS_H
 #  include <windows.h>
+#else
+#  include <netinet/in.h>       // htonl() ntohl()
 #endif
 
 #include <iostream>