diff --git a/doc/Makefile b/doc/Makefile
index 2f8b3f18495d80..51c4f3f51405c4 100644
--- a/doc/Makefile
+++ b/doc/Makefile
@@ -28,7 +28,7 @@ DOCUMENTER_OPTIONS := linkcheck=$(linkcheck) doctest=$(doctest) buildroot=$(call
 UNICODE_DATA_VERSION=13.0.0
 $(SRCCACHE)/UnicodeData-$(UNICODE_DATA_VERSION).txt:
 	@mkdir -p "$(SRCCACHE)"
-	$(JLDOWNLOAD) "$@" http://www.unicode.org/Public/$(UNICODE_DATA_VERSION)/ucd/UnicodeData.txt
+	$(JLDOWNLOAD) "$@" https://www.unicode.org/Public/$(UNICODE_DATA_VERSION)/ucd/UnicodeData.txt
 
 deps: $(SRCCACHE)/UnicodeData-$(UNICODE_DATA_VERSION).txt
 	$(JLCHECKSUM) "$<"