diff --git a/config.mk b/config.mk
index 07a33da..9b56f8a 100644
--- a/config.mk
+++ b/config.mk
@@ -10,6 +10,12 @@ MANPREFIX = ${PREFIX}/share/man
 X11INC = /usr/X11R6/include
 X11LIB = /usr/X11R6/lib
 
+# Uncomment for BSD
+#BSD=-D_BSD_SOURCE
+
+# Uncomment for NetBSD
+#NETBSD=-D_NETBSD_SOURCE
+
 # Uncomment for message patch / MESSAGE_PATCH / COLORMESSAGE_PATCH / DWM_LOGO_PATCH
 #XINERAMA=-lXinerama
 #XINERAMAFLAGS = -DXINERAMA
@@ -25,7 +31,7 @@ INCS = -I. -I/usr/include -I${X11INC}
 LIBS = -L/usr/lib -lc -lcrypt -L${X11LIB} -lX11 -lXext -lXrandr ${XINERAMA} ${PAM} ${IMLIB}
 
 # flags
-CPPFLAGS = -DVERSION=\"${VERSION}\" -D_DEFAULT_SOURCE -DHAVE_SHADOW_H ${XINERAMAFLAGS}
+CPPFLAGS = -DVERSION=\"${VERSION}\" -D_DEFAULT_SOURCE -DHAVE_SHADOW_H ${XINERAMAFLAGS} ${BSD} ${NETBSD}
 CFLAGS = -std=c99 -pedantic -Wall -Os ${INCS} ${CPPFLAGS}
 LDFLAGS = -s ${LIBS}
 COMPATSRC = explicit_bzero.c