diff -r 31ad7885e2e5 Makefile.pre.in
--- a/Makefile.pre.in	Sun Jun 05 10:50:16 2016 +0300
+++ b/Makefile.pre.in	Sun Jun 05 14:05:14 2016 +0100
@@ -792,12 +792,16 @@
 	@$(MKDIR_P) Include
 	if test "$(cross_compiling)" != "yes"; then \
 		$(PGEN) $(GRAMMAR_INPUT) $(GRAMMAR_H) $(GRAMMAR_C); \
+	elif test $(srcdir)/Include/graminit.h -ef $(GRAMMAR_H); then \
+		touch $(GRAMMAR_H); \
 	else \
 		cp $(srcdir)/Include/graminit.h $(GRAMMAR_H); \
 	fi
 $(GRAMMAR_C): $(GRAMMAR_H)
 	if test "$(cross_compiling)" != "yes"; then \
 		touch $(GRAMMAR_C); \
+	elif test $(srcdir)/Python/graminit.c -ef $(GRAMMAR_C); then \
+		touch $(GRAMMAR_C); \
 	else \
 		cp $(srcdir)/Python/graminit.c $(GRAMMAR_C); \
 	fi