diff --git a/mboxd.c b/mboxd.c
index 059261b..04b2cb6 100644
--- a/mboxd.c
+++ b/mboxd.c
@@ -255,7 +255,8 @@
 			case '\0':
 				break;
 			case 'M':
-				context->backend.flash_size <<= 10;
+				context->backend.flash_size <<= 20;
+				break;
 			case 'K':
 				context->backend.flash_size <<= 10;
 				break;