--- dwm.c
+++ dwm.c
@@ -199,6 +199,7 @@ static void sendmon(Client *c, Monitor *m);
 static void setclientstate(Client *c, long state);
 static void setfocus(Client *c);
 static void setfullscreen(Client *c, int fullscreen);
+static void fullscreen(const Arg *arg);
 static void setlayout(const Arg *arg);
 static void setmfact(const Arg *arg);
 static void setup(void);