diff --git a/ext/rbconfig/sizeof/extconf.rb b/ext/rbconfig/sizeof/extconf.rb
index 619b4256f8..ac66b6ac26 100644
--- a/ext/rbconfig/sizeof/extconf.rb
+++ b/ext/rbconfig/sizeof/extconf.rb
@@ -1,2 +1,3 @@
 $srcs = %w[sizes.c]
+$distcleanfiles.concat($srcs)
 create_makefile('rbconfig/sizeof')