From 5a0166489e7d4ec6ce70fc20070f667fd00bccec Mon Sep 17 00:00:00 2001
From: Scott Lahteine <github@thinkyhead.com>
Date: Sat, 30 Oct 2021 22:43:02 -0500
Subject: [PATCH] =?UTF-8?q?=F0=9F=A9=B9=20Fix=20linker=20error=20(transfer?=
 =?UTF-8?q?=5Fport=5Findex)?=
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---
 Marlin/src/sd/cardreader.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Marlin/src/sd/cardreader.cpp b/Marlin/src/sd/cardreader.cpp
index 1ab6dcc7c6..513d682de6 100644
--- a/Marlin/src/sd/cardreader.cpp
+++ b/Marlin/src/sd/cardreader.cpp
@@ -72,8 +72,8 @@ char CardReader::filename[FILENAME_LENGTH], CardReader::longFilename[LONG_FILENA
 
 IF_DISABLED(NO_SD_AUTOSTART, uint8_t CardReader::autofile_index); // = 0
 
-#if BOTH(HAS_MULTI_SERIAL, BINARY_FILE_TRANSFER)
-  serial_index_t CardReader::transfer_port_index;
+#if ENABLED(BINARY_FILE_TRANSFER)
+  serial_index_t IF_DISABLED(HAS_MULTI_SERIAL, constexpr) CardReader::transfer_port_index;
 #endif
 
 // private: