diff --git a/Makefile b/Makefile
index db77256f..62c52de4 100644
--- a/Makefile
+++ b/Makefile
@@ -42,7 +42,8 @@ $(NAME)-%.$(EXT): $(SRCDIR)/$(NAME)-%.sfdir $(SRCDIR)/$(LATIN)-%.sfdir $(SRCDIR)
 	@FILES=($+); $(PY) $(BUILD) --version=$(VERSION) --out-file=$@ --feature-file=$${FILES[2]} $${FILES[0]} $${FILES[1]}
 ifeq ($(ttx), true)
 	@echo "   TTX	$@"
-	@pyftsubset $@ --output-file=$@ --unicodes='*' --layout-features='*' --name-IDs='*'
+	@pyftsubset $@ --output-file=$@.tmp --unicodes='*' --layout-features='*' --name-IDs='*' --notdef-outline
+	@mv $@.tmp $@
 endif
 ifeq ($(crunch), true)
 	@echo "   FC	$@"