diff --git a/target/linux/ramips/image/mt7621.mk b/target/linux/ramips/image/mt7621.mk
index 50c53a6d8e..a5db519995 100644
--- a/target/linux/ramips/image/mt7621.mk
+++ b/target/linux/ramips/image/mt7621.mk
@@ -223,6 +223,7 @@ endef
 define Build/zytrx-header
 	$(eval board=$(word 1,$(1)))
 	$(eval version=$(word 2,$(1)))
+	$(eval version=$(shell echo $(version) | cut -c 1-31))
 	$(STAGING_DIR_HOST)/bin/zytrx -B '$(board)' -v '$(version)' -i $@ -o $@.new
 	mv $@.new $@
 endef