diff --git a/ext/stringio/depend b/ext/stringio/depend
new file mode 100644
index 0000000000..cc9eae3f55
--- /dev/null
+++ b/ext/stringio/depend
@@ -0,0 +1,2 @@
+stringio.o: stringio.c $(hdrdir)/ruby.h $(topdir)/config.h \
+  $(hdrdir)/defines.h $(hdrdir)/intern.h $(hdrdir)/rubyio.h