diff --git a/Makefile b/Makefile
index 504327207d66e4b2b02bed3de555dc6330992b7a..cbab0dc53065d93f314763d21201eb23aa002d70 100644
--- a/Makefile
+++ b/Makefile
@@ -129,6 +129,11 @@ endif
 $(if $(word 2, $(KBUILD_EXTMOD)), \
 	$(error building multiple external modules is not supported))
 
+# Remove trailing slashes
+ifneq ($(filter %/, $(KBUILD_EXTMOD)),)
+KBUILD_EXTMOD := $(shell dirname $(KBUILD_EXTMOD).)
+endif
+
 export KBUILD_EXTMOD
 
 # Kbuild will save output files in the current working directory.