diff --git a/scripts/_common.sh b/scripts/_common.sh
index bac71f7..baa3636 100644
--- a/scripts/_common.sh
+++ b/scripts/_common.sh
@@ -36,20 +36,6 @@ bool_to_true_false () {
 # EXPERIMENTAL HELPERS
 #=================================================
 
-# Check if the device of the main mountpoint "/" is an SD card
-#
-# return 1 if it's an SD card, else 0
-_ynh_is_main_device_is_sd_card () {
-	local main_device=$(lsblk --output PKNAME --noheadings $(findmnt / --nofsroot --uniq --output source --noheadings --first-only))
-
-	if echo $main_device | grep --quiet "mmc" && [ $(cat /sys/block/$main_device/queue/rotational) -eq 0 ]
-	then
-		return 1
-	else
-		return 0
-	fi
-}
-
 # Add swap
 #
 # usage: ynh_add_swap --size=SWAP in Mb
@@ -70,7 +56,7 @@ ynh_add_swap () {
  	SD_CARD_CAN_SWAP=${SD_CARD_CAN_SWAP:-0}
 
 	# Swap on SD card only if it's is specified
-	if [ _ynh_is_main_device_is_sd_card ] && [ "$SD_CARD_CAN_SWAP" == "0" ]
+	if ynh_is_main_device_is_sd_card && [ "$SD_CARD_CAN_SWAP" == "0" ]
 	then
 		return
 	fi
@@ -122,6 +108,22 @@ ynh_del_swap () {
 	fi
 }
 
+# Check if the device of the main mountpoint "/" is an SD card
+#
+# [internal]
+#
+# return 0 if it's an SD card, else 1
+ynh_is_main_device_is_sd_card () {
+	local main_device=$(lsblk --output PKNAME --noheadings $(findmnt / --nofsroot --uniq --output source --noheadings --first-only))
+
+	if echo $main_device | grep --quiet "mmc" && [ $(tail -n1 /sys/block/$main_device/queue/rotational) == "0" ]
+	then
+		return 0
+	else
+		return 1
+	fi
+}
+
 # Check the amount of available RAM
 #
 # usage: ynh_check_ram [--required=RAM required in Mb] [--no_swap|--only_swap] [--free_ram]