diff --git a/target/linux/ramips/image/Makefile b/target/linux/ramips/image/Makefile
index 6eef596caf..145dbf4ec5 100644
--- a/target/linux/ramips/image/Makefile
+++ b/target/linux/ramips/image/Makefile
@@ -10,6 +10,7 @@ include $(INCLUDE_DIR)/image.mk
 DEVICE_VARS += DTS IMAGE_SIZE NETGEAR_BOARD_ID NETGEAR_HW_ID
 DEVICE_VARS += BUFFALO_TAG_PLATFORM BUFFALO_TAG_VERSION BUFFALO_TAG_MINOR
 DEVICE_VARS += SEAMA_SIGNATURE SEAMA_MTDBLOCK
+DEVICE_VARS += SERCOMM_HWID SERCOMM_HWVER SERCOMM_SWVER
 
 loadaddr-y := 0x80000000
 loadaddr-$(CONFIG_TARGET_ramips_rt288x) := 0x88000000
@@ -132,6 +133,19 @@ define Build/zyimage
 	$(STAGING_DIR_HOST)/bin/zyimage $(1) $@
 endef
 
+define Build/sercom-seal
+	$(STAGING_DIR_HOST)/bin/mksercommfw \
+		-i $@ \
+		-b $(SERCOMM_HWID) \
+		-r $(SERCOMM_HWVER) \
+		-v $(SERCOMM_SWVER) \
+		$(1)
+endef
+
+define Build/sercom-footer
+	$(call Build/sercom-seal,-f)
+endef
+
 ralink_default_fw_size_4M=3866624
 ralink_default_fw_size_8M=8060928
 ralink_default_fw_size_16M=16121856
diff --git a/target/linux/ramips/image/mt7621.mk b/target/linux/ramips/image/mt7621.mk
index 9e42404f64..671e7f378a 100644
--- a/target/linux/ramips/image/mt7621.mk
+++ b/target/linux/ramips/image/mt7621.mk
@@ -531,7 +531,16 @@ TARGET_DEVICES += mqmaker_witi-512m
 
 define Device/wndr3700v5
   DTS := WNDR3700V5
-  IMAGE_SIZE := $(ralink_default_fw_size_16M)
+  BLOCKSIZE := 64k
+  IMAGE_SIZE := 15232k
+  SERCOMM_HWID := AYB
+  SERCOMM_HWVER := A001
+  SERCOMM_SWVER := 0x1054
+  IMAGES += factory.img
+  IMAGE/default := append-kernel | pad-to $$$$(BLOCKSIZE) | append-rootfs | pad-rootfs
+  IMAGE/sysupgrade.bin := $$(IMAGE/default) | append-metadata | check-size $$$$(IMAGE_SIZE)
+  IMAGE/factory.img := pad-extra 320k | $$(IMAGE/default) | pad-to $$$$(BLOCKSIZE) | \
+	sercom-footer | pad-to 128 | zip WNDR3700v5.bin | sercom-seal
   DEVICE_TITLE := Netgear WNDR3700v5
   DEVICE_PACKAGES := kmod-mt7603 kmod-mt76x2 kmod-usb3 wpad-basic
 endef
diff --git a/target/linux/ramips/image/mt76x8.mk b/target/linux/ramips/image/mt76x8.mk
index 0fd72a4117..22d79bad39 100644
--- a/target/linux/ramips/image/mt76x8.mk
+++ b/target/linux/ramips/image/mt76x8.mk
@@ -2,22 +2,6 @@
 # MT76x8 Profiles
 #
 
-DEVICE_VARS += SERCOMM_HWID SERCOMM_HWVER SERCOMM_SWVER
-
-define Build/sercom-seal
-	$(STAGING_DIR_HOST)/bin/mksercommfw \
-		-i $@ \
-		-b $(SERCOMM_HWID) \
-		-r $(SERCOMM_HWVER) \
-		-v $(SERCOMM_SWVER) \
-		$(1)
-endef
-
-define Build/sercom-footer
-	$(call Build/sercom-seal,-f)
-endef
-
-
 define Device/tplink
   TPLINK_FLASHLAYOUT :=
   TPLINK_HWID :=