diff --git a/Makefile b/Makefile
index 49597e020f..e8e7b57fb5 100644
--- a/Makefile
+++ b/Makefile
@@ -442,7 +442,7 @@ $(obj)/project_filelist.txt:
 		echo "*** Error: Project must be built before generating file list ***"; \
 		exit 1; \
 	fi
-	find $(obj) -path "$(obj)/util" -prune -o -name "*.d" -exec cat {} \; | \
+	find $(obj) -path "$(obj)/util" -prune -o -path "$(obj)/external" -prune -o -name "*.d" -exec cat {} \; | \
 	  sed "s|$(top)/||" | sed 's/[:\\]/ /g' | sed 's/ /\n/g' | sort | uniq | \
 	  grep -v '\.o$$' > $(obj)/project_filelist.txt