diff --git a/Makefile b/Makefile
index 44e28ba802..eb6d627dae 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,4 @@
-BUILD_DIRS="build.*"
+BUILD_DIRS=build.*
 
 all: system
 
@@ -9,7 +9,7 @@ release:
 	./scripts/image release
 
 clean:
-	rm -rf $(BUILD_DIRS)
+	rm -rf $(BUILD_DIRS)/* $(BUILD_DIRS)/.stamps
 
 src-pkg:
 	tar cvjf sources.tar.bz2 sources .stamps