-T (treat DEST as a normal file) is not supported by BSD install(1)

--- Makefile.orig	2020-09-12 17:23:57 UTC
+++ Makefile
@@ -413,7 +413,7 @@ endif
 install-bashcompletion:
 ifneq ($(BASHCOMPLETIONSDIR),)
 	$(INSTALL) -d $(DESTDIR)$(BASHCOMPLETIONSDIR)
-	$(INSTALL) -m 644 -T $(SRCPATH)/tools/bash-autocomplete.sh $(DESTDIR)$(BASHCOMPLETIONSDIR)/x264
+	$(INSTALL) -m 644 $(SRCPATH)/tools/bash-autocomplete.sh $(DESTDIR)$(BASHCOMPLETIONSDIR)/x264
 endif
 
 uninstall: