diff --git a/Makefile b/Makefile
index 6f2fcd7..b0a3136 100644
--- a/Makefile
+++ b/Makefile
@@ -34,5 +34,6 @@ prove:
 clean:
 	@echo [clean]
 	rm -f quox quox-tests result
+	rm -rf lib/build main/build tests/build
 
 .SILENT: