diff --git a/ext/rbconfig/sizeof/depend b/ext/rbconfig/sizeof/depend
index 5dbe49298f..5fa99ad13d 100644
--- a/ext/rbconfig/sizeof/depend
+++ b/ext/rbconfig/sizeof/depend
@@ -1,15 +1,17 @@
-limits.c: $(top_srcdir)/tool/generic_erb.rb $(top_srcdir)/template/limits.c.tmpl
+# sources
+
+{$(VPATH)}limits.c: $(top_srcdir)/tool/generic_erb.rb $(top_srcdir)/template/limits.c.tmpl
 	$(Q) $(RUBY) $(top_srcdir)/tool/generic_erb.rb --output=$@ \
 		$(top_srcdir)/template/limits.c.tmpl \
 
-sizes.c: $(top_srcdir)/tool/generic_erb.rb \
+{$(VPATH)}sizes.c: $(top_srcdir)/tool/generic_erb.rb \
 		   $(top_srcdir)/template/sizes.c.tmpl \
 		   $(top_srcdir)/configure.in \
 		   $(top_srcdir)/ext/rbconfig/sizeof/extconf.rb
 	$(Q) $(RUBY) $(top_srcdir)/tool/generic_erb.rb --output=$@ \
 		$(top_srcdir)/template/sizes.c.tmpl \
-                $(top_srcdir)/configure.in \
-                $(top_srcdir)/ext/rbconfig/sizeof/extconf.rb
+		$(top_srcdir)/configure.in \
+		$(top_srcdir)/ext/rbconfig/sizeof/extconf.rb
 
 # AUTOGENERATED DEPENDENCIES START
 sizes.o: $(RUBY_EXTCONF_H)