diff --git a/installing/installation-guide.md b/installing/installation-guide.md
index 0c8ad8c4..e0b97bbd 100644
--- a/installing/installation-guide.md
+++ b/installing/installation-guide.md
@@ -65,7 +65,7 @@ an installation medium.)
 If you prefer to use a USB drive, then you just need to copy the ISO onto the
 USB device, e.g. using `dd`:
 
-    dd if=Qubes-R3-x86_64.iso of=/dev/sdX
+    dd if=Qubes-R3-x86_64.iso of=/dev/sdX bs=1M
 
 Change `Qubes-R3-x86_64.iso` to the filename of the version you're installing,
 and change `/dev/sdX` to the correct target device (e.g., `/dev/sda`).