diff --git a/common.mk b/common.mk
index 6d0d3303c0..1d8a362235 100644
--- a/common.mk
+++ b/common.mk
@@ -886,8 +886,10 @@ $(srcdir)/ext/json/parser/parser.c: $(srcdir)/ext/json/parser/parser.rl
 	$(Q) $(CHDIR) $(@D) && $(exec) $(MAKE) -f prereq.mk $(MFLAGS) \
 		Q=$(Q) ECHO=$(ECHO) top_srcdir=../../.. srcdir=. VPATH=../../.. BASERUBY="$(BASERUBY)"
 
-$(srcdir)/ext/rbconfig/sizeof/sizes.c: $(srcdir)/ext/rbconfig/sizeof/depend \
+{$(VPATH)}ext/rbconfig/sizeof/sizes.c: $(srcdir)/ext/rbconfig/sizeof/depend \
 		$(srcdir)/tool/generic_erb.rb $(srcdir)/template/sizes.c.tmpl $(srcdir)/configure.in
+
+ext/rbconfig/sizeof/sizes.c:
 	$(ECHO) generating $@
 	$(Q) $(CHDIR) $(@D) && \
 	sed '/AUTOGENERATED/q;s#{.*}##' depend | \
diff --git a/ext/rbconfig/sizeof/depend b/ext/rbconfig/sizeof/depend
index 4243785d43..f081b177af 100644
--- a/ext/rbconfig/sizeof/depend
+++ b/ext/rbconfig/sizeof/depend
@@ -1,4 +1,4 @@
-{$(VPATH)}sizes.c: $(top_srcdir)/tool/generic_erb.rb \
+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