diff --git a/runtime/doc/Makefile b/runtime/doc/Makefile
index 4112ae9..fcbcdc5 100644
--- a/runtime/doc/Makefile
+++ b/runtime/doc/Makefile
@@ -396,7 +396,7 @@
 	vim -S test_urls.vim
 
 clean:
-	-rm doctags *.html tags.ref
+	-rm -f doctags *.html tags.ref
 
 # These files are in the extra archive, skip if not present