diff --git a/Makefile b/Makefile
index ef3bf09..2fb13ae 100644
--- a/Makefile
+++ b/Makefile
@@ -10,7 +10,6 @@ all: options st
 
 options:
 	@echo st build options:
-	@echo "SYSTEM   = ${SYSTEM}"
 	@echo "CFLAGS   = ${CFLAGS}"
 	@echo "LDFLAGS  = ${LDFLAGS}"
 	@echo "CC       = ${CC}"
diff --git a/config.mk b/config.mk
index f0c7e2e..46efc0c 100644
--- a/config.mk
+++ b/config.mk
@@ -14,15 +14,8 @@ X11LIB = /usr/X11R6/lib
 INCS = -I. -I/usr/include -I${X11INC}
 LIBS = -L/usr/lib -lc -L${X11LIB} -lX11 -lutil
 
-# uncomment manualy your system if compilation fail
-SYSTEM = -D`uname | tr a-z A-Z`
-#SYSTEM = -DLINUX
-#SYSTEM = -DOPENBSD
-#SYSTEM = -DFREEBSD
-#SYSTEM = -DNETBSD
-
 # flags
-CPPFLAGS = -DVERSION=\"${VERSION}\" ${SYSTEM}
+CPPFLAGS = -DVERSION=\"${VERSION}\"
 CFLAGS = -std=c99 -pedantic -Wall -Os ${INCS} ${CPPFLAGS}
 LDFLAGS = -s ${LIBS}
 
diff --git a/st.c b/st.c
index af3ec6d..f42797f 100644
--- a/st.c
+++ b/st.c
@@ -20,11 +20,11 @@
 #include <X11/keysym.h>
 #include <X11/Xutil.h>
 
-#if   defined(LINUX)
+#if   defined(__linux)
  #include <pty.h>
-#elif defined(OPENBSD) || defined(NETBSD)
+#elif defined(__OpenBSD__) || defined(__NetBSD__)
  #include <util.h>
-#elif defined(FREEBSD)
+#elif defined(__FreeBSD__) || defined(__DragonFly__)
  #include <libutil.h>
 #endif