diff --git a/ext/rbconfig/sizeof/depend b/ext/rbconfig/sizeof/depend
index 360b3386d3..c8106dd123 100644
--- a/ext/rbconfig/sizeof/depend
+++ b/ext/rbconfig/sizeof/depend
@@ -1,3 +1,3 @@
-sizes.c: $(top_srcdir)/tool/generic_erb.rb $(top_srcdir)/template/sizes.c.tmpl $(top_srcdir)/configure.in
+{$(srcdir)}sizes.c: $(top_srcdir)/tool/generic_erb.rb $(top_srcdir)/template/sizes.c.tmpl $(top_srcdir)/configure.in
 	$(Q) $(RUBY) $(top_srcdir)/tool/generic_erb.rb --output=$@ \
 		$(top_srcdir)/template/sizes.c.tmpl $(top_srcdir)/configure.in