diff --git a/target/linux/mvebu/image/Makefile b/target/linux/mvebu/image/Makefile
index 108b569c07..9084b3e028 100644
--- a/target/linux/mvebu/image/Makefile
+++ b/target/linux/mvebu/image/Makefile
@@ -42,25 +42,19 @@ define Build/boot-img-ext4
 endef
 
 define Build/sdcard-img
-	if [ -n "$(UBOOT)" ]; then UBOOT="$(STAGING_DIR_IMAGE)/$(UBOOT)"; fi; \
-	BOOTFS_SIZE=$$(( $(CONFIG_TARGET_KERNEL_PARTSIZE) * 1024 * 2 )); \
-	ROOTFS_SIZE=$$(( $(CONFIG_TARGET_ROOTFS_PARTSIZE) * 1024 * 2 )); \
 	SIGNATURE="$(SIGNATURE)" \
 	./gen_mvebu_sdcard_img.sh $@ \
-		$$UBOOT \
-		c $$BOOTFS_SIZE $@.boot \
-		83 $$ROOTFS_SIZE $(IMAGE_ROOTFS)
+		$(if $(UBOOT),$(STAGING_DIR_IMAGE)/$(UBOOT)) \
+		c $(CONFIG_TARGET_KERNEL_PARTSIZE) $@.boot \
+		83 $(CONFIG_TARGET_ROOTFS_PARTSIZE) $(IMAGE_ROOTFS)
 endef
 
 define Build/sdcard-img-ext4
-	if [ -n "$(UBOOT)" ]; then UBOOT="$(STAGING_DIR_IMAGE)/$(UBOOT)"; fi; \
-	BOOTFS_SIZE=$$(( $(CONFIG_TARGET_KERNEL_PARTSIZE) * 1024 * 2 )); \
-	ROOTFS_SIZE=$$(( $(CONFIG_TARGET_ROOTFS_PARTSIZE) * 1024 * 2 )); \
 	SIGNATURE="$(SIGNATURE)" \
 	./gen_mvebu_sdcard_img.sh $@ \
-		$$UBOOT \
-		83 $$BOOTFS_SIZE $@.bootimg \
-		83 $$ROOTFS_SIZE $(IMAGE_ROOTFS)
+		$(if $(UBOOT),$(STAGING_DIR_IMAGE)/$(UBOOT)) \
+		83 $(CONFIG_TARGET_KERNEL_PARTSIZE) $@.bootimg \
+		83 $(CONFIG_TARGET_ROOTFS_PARTSIZE) $(IMAGE_ROOTFS)
 endef
 
 define Build/omnia-medkit-initramfs
diff --git a/target/linux/mvebu/image/gen_mvebu_sdcard_img.sh b/target/linux/mvebu/image/gen_mvebu_sdcard_img.sh
index 67416ed80c..e0230e48b6 100755
--- a/target/linux/mvebu/image/gen_mvebu_sdcard_img.sh
+++ b/target/linux/mvebu/image/gen_mvebu_sdcard_img.sh
@@ -18,7 +18,7 @@
 #
 
 usage() {
-	echo "$0 <outfile> [<bootloader> <type_partitionN> <sectors_partitionN> <img_partitionN>]?"
+	echo "$0 <outfile> [<bootloader> <type_partitionN> <size_partitionN> <img_partitionN>]?"
 }
 
 # always require first 2 or 3 arguments
@@ -46,7 +46,7 @@ dd if=/dev/zero of="$OUTFILE" bs=512 count=1 >/dev/null
 printf "Done\n"
 
 while [ "$#" -ge 3 ]; do
-	ptgen_args="$ptgen_args -t $1 -p $(($2 / 2 + 256))"
+	ptgen_args="$ptgen_args -t $1 -p $(($2 * 1024 + 256))"
 	parts="$parts$3 "
 	shift; shift; shift
 done