diff --git a/doomgeneric/Makefile b/doomgeneric/Makefile
index f1d8df5..a35d5fb 100644
--- a/doomgeneric/Makefile
+++ b/doomgeneric/Makefile
@@ -15,7 +15,7 @@ endif
 CC=gcc  # gcc or g++
 CFLAGS+=-ggdb3 -Os
 LDFLAGS+=-Wl,--gc-sections
-CFLAGS+=-ggdb3 -Wall -DNORMALUNIX -DLINUX -DSNDSERV # -DUSEASM
+CFLAGS+=-ggdb3 -Wall -DNORMALUNIX -DLINUX -DSNDSERV -D_DEFAULT_SOURCE # -DUSEASM
 LIBS+=-lm -lc -lX11
 
 # subdirectory for objects