diff --git a/tools/build.sh b/tools/build.sh
index f05b210d4c6d83d1900d84ec78e8385062cc43f1..1a1effc9eea40dab6c45523623bd52612dad91ac 100755
--- a/tools/build.sh
+++ b/tools/build.sh
@@ -178,7 +178,7 @@ BUILD_WORLD2=
 buildit
 
 TARGET=$BASE-4
-#CLEAN_FLAGS="-K all"
+CLEAN_FLAGS="-K all"
 OLDLISP="${BASE}-3/lisp/lisp -noinit $FPU_MODE"
 ENABLE=$ENABLE4