diff --git a/assembler/src/Makefile.am b/assembler/src/Makefile.am
index 737e9367..c42c2be6 100644
--- a/assembler/src/Makefile.am
+++ b/assembler/src/Makefile.am
@@ -1,3 +1,5 @@
+AM_YFLAGS = -d
+
 bin_PROGRAMS = gen4asm
 
 gen4asm_SOURCES = \
@@ -8,4 +10,9 @@ gen4asm_SOURCES = \
 	lex.l \
 	main.c
 
+gram.h: gram.c
+
+BUILT_SOURCES = gram.h gram.c lex.c
+MAINTAINERCLEANFILES = $(BUILT_SOURCES)
+
 # man_MANS = gen4asm.1