diff --git a/gc/mmtk/extconf.rb b/gc/mmtk/extconf.rb
index c0e788037ec..8329ef62b19 100644
--- a/gc/mmtk/extconf.rb
+++ b/gc/mmtk/extconf.rb
@@ -5,7 +5,7 @@ require_relative "../extconf_base"
 # Statically link `libmmtk_ruby.a`
 $LIBS << " $(MMTK_BUILD)/$(LIBMMTK_RUBY)"
 
-rustsrcs = Dir.glob("src/*.rs", base: __dir__).map {|s| "$(srcdir)/#{s}"}
+rustsrcs = Dir.glob("src/**/*.rs", base: __dir__).map {|s| "$(srcdir)/#{s}"}
 
 create_gc_makefile("mmtk") do |makefile|
   [