diff --git a/usr.bin/m4/main.c b/usr.bin/m4/main.c
index 1a0011d6cf2..3ebbaa3a1a0 100644
--- a/usr.bin/m4/main.c
+++ b/usr.bin/m4/main.c
@@ -174,8 +174,6 @@ static int do_look_ahead(int, const char *);
 
 static void enlarge_stack(void);
 
-int main(int, char *[]);
-
 int
 main(int argc, char *argv[])
 {