diff --git a/Makefile b/Makefile
index 98d32c046c..502991f658 100644
--- a/Makefile
+++ b/Makefile
@@ -119,6 +119,11 @@ ifeq ($(BR2_EXTERNAL),)
   override BR2_EXTERNAL = support/dummy-external
   $(shell rm -f $(BR2_EXTERNAL_FILE))
 else
+  _BR2_EXTERNAL = $(shell cd $(BR2_EXTERNAL) >/dev/null 2>&1 && pwd)
+  ifeq ($(_BR2_EXTERNAL),)
+    $(error BR2_EXTERNAL='$(BR2_EXTERNAL)' does not exist, relative to $(TOPDIR))
+  endif
+  override BR2_EXTERNAL := $(_BR2_EXTERNAL)
   $(shell echo BR2_EXTERNAL ?= $(BR2_EXTERNAL) > $(BR2_EXTERNAL_FILE))
 endif