-IMG_PREFIX:=openwrt-$(if $(CONFIG_VERSION_FILENAMES),$(VERSION_NUMBER)-)$(BOARD)$(if $(SUBTARGET),-$(SUBTARGET))
+sanitize = $(call tolower,$(subst _,-,$(1)))
+
+DIST_SANITIZED:=$(call sanitize,$(VERSION_DIST))
+EXTRA_NAME_SANITIZED=$(call sanitize,$(EXTRA_IMAGE_NAME))
+
+IMG_PREFIX:=$(DIST_SANITIZED)-$(if $(CONFIG_VERSION_FILENAMES),$(VERSION_NUMBER)-)$(if $(EXTRA_NAME_SANITIZED),$(EXTRA_NAME_SANITIZED)-)$(BOARD)$(if $(SUBTARGET),-$(SUBTARGET))