diff --git a/ext/etc/depend b/ext/etc/depend
index 6fc0ce8c91..a73a18465a 100644
--- a/ext/etc/depend
+++ b/ext/etc/depend
@@ -1,4 +1,5 @@
 etc.o : etc.c constdefs.h $(HDRS) $(ruby_headers) \
+  $(hdrdir)/ruby/io.h \
   $(hdrdir)/ruby/encoding.h \
   $(hdrdir)/ruby/oniguruma.h