# Modules built outside the kernel source tree go into extra by default
INSTALL_MOD_DIR ?= extra
-ext-mod-dir = $(INSTALL_MOD_DIR)$(subst $(KBUILD_EXTMOD),,$(@D))
+ext-mod-dir = $(INSTALL_MOD_DIR)$(subst $(patsubst %/,%,$(KBUILD_EXTMOD)),,$(@D))
modinst_dir = $(if $(KBUILD_EXTMOD),$(ext-mod-dir),kernel/$(@D))