diff --git a/pmb/parse/arguments.py b/pmb/parse/arguments.py
index 044450fa..b89c4850 100644
--- a/pmb/parse/arguments.py
+++ b/pmb/parse/arguments.py
@@ -115,7 +115,8 @@ def arguments_initfs(subparser):
 def arguments_qemu(subparser):
     ret = subparser.add_parser("qemu")
     ret.add_argument("--cmdline", help="override kernel commandline")
-    ret.add_argument("--image-size", help="set rootfs size (e.g. 2048M or 2G)")
+    ret.add_argument("--image-size", default="4G",
+                     help="set rootfs size, e.g. 2048M or 2G (default: 4G)")
     ret.add_argument("-m", "--memory", type=int, default=1024,
                      help="guest RAM (default: 1024)")
     ret.add_argument("-p", "--port", type=int, default=2222,