--- a/Makefile
+++ b/Makefile
@@ -29,6 +29,8 @@
 	    sed -e 's/Char \([a-zA-Z0-9_]*\)\(.*\)/extern Char \1[];/' | \
 	    sort >> $@
 
+.depend alloc.o: const.h error.h
+
 BUILDFIRST = const.h error.h
 
 .include <bsd.prog.mk>