diff --git a/common b/common
index da86cd91..78ac6544 100644
--- a/common
+++ b/common
@@ -247,6 +247,11 @@ s/ .*//p
 	    usage
 	    ;;
 
+	--extra-space=*)
+	    export SCRATCH_DEV_EMPTY_SPACE=${r#*=}
+	    xpand=false
+	    ;;
+
 	*)
 	    start=$r
 	    end=$r