--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -8,6 +8,8 @@
 AM_YFLAGS = -d -p `${SED} -n 's/.*_\(.*\)/\1_/p' <<<"$*"`
 AM_LFLAGS = -o lex.yy.c
 
+lex_rtree.l: parse_rtree.h
+lex_utree.l: parse_utree.h
 __top_builddir__bin_mptp_LDADD = libparse_utree.a libparse_rtree.a
 __top_builddir__bin_mptp_SOURCES = arch.c \
 auto.c \