diff --git a/builder/Makefile.am b/builder/Makefile.am
index a0d139bad..29f755624 100644
--- a/builder/Makefile.am
+++ b/builder/Makefile.am
@@ -309,7 +309,7 @@ CLEANFILES += \
 if HAVE_OCAML
 # Automake-generated makefile has a rule ".y.c" but lacks a rule ".y.h".
 index-parse.h: index-parse.y
-	touch index-parse.y
+	touch $(srcdir)/index-parse.y
 	$(MAKE) index-parse.c
 # Also it doesn't generate dependencies for the C files that include
 # index-parse.h.