diff --git a/src/toolsComm/flex/Makefile.Unix b/src/toolsComm/flex/Makefile.Unix
index 4bf711b40..c9009210e 100644
--- a/src/toolsComm/flex/Makefile.Unix
+++ b/src/toolsComm/flex/Makefile.Unix
@@ -11,7 +11,7 @@ SKELETON_FILE=include/flex.skel.static
 ifeq ($(T_A),hp700)
 USR_CFLAGS = -DDEFAULT_SKELETON_FILE=\"$(SKELETON_FILE)\" -DSCO_UNIX
 else
-USR_CFLAGS = -DDEFAULT_SKELETON_FILE=\"$(SKELETON_FILE)\"
+USR_CFLAGS = -DDEFAULT_SKELETON_FILE=\"$(SKELETON_FILE)\" -DUSG
 endif
 USR_LDLIBS = -s