diff --git a/package/base-files/files/lib/functions.sh b/package/base-files/files/lib/functions.sh
index e56e4637f0..ee0c33845c 100644
--- a/package/base-files/files/lib/functions.sh
+++ b/package/base-files/files/lib/functions.sh
@@ -331,13 +331,19 @@ find_mtd_part() {
 }
 
 find_mmc_part() {
-	local DEVNAME PARTNAME
+	local DEVNAME PARTNAME ROOTDEV
 
 	if grep -q "$1" /proc/mtd; then
 		echo "" && return 0
 	fi
 
-	for DEVNAME in /sys/block/mmcblk*/mmcblk*p*; do
+	if [ -n "$2" ]; then
+		ROOTDEV="$2"
+	else
+		ROOTDEV="mmcblk*"
+	fi
+
+	for DEVNAME in /sys/block/$ROOTDEV/mmcblk*p*; do
 		PARTNAME="$(grep PARTNAME ${DEVNAME}/uevent | cut -f2 -d'=')"
 		[ "$PARTNAME" = "$1" ] && echo "/dev/$(basename $DEVNAME)" && return 0
 	done