diff --git a/doc/src/sgml/Makefile b/doc/src/sgml/Makefile
index 8326c7c6736..2420c556815 100644
--- a/doc/src/sgml/Makefile
+++ b/doc/src/sgml/Makefile
@@ -171,7 +171,7 @@ postgres.pdf:
 epub: postgres.epub
 postgres.epub: postgres.sgml $(ALLSGML)
 	$(XMLLINT) --noout --valid $<
-	$(DBTOEPUB) $<
+	$(DBTOEPUB) -o $@ $<
 
 
 ##