diff --git a/doc/src/sgml/Makefile b/doc/src/sgml/Makefile
index 11aac913812..71798b0b213 100644
--- a/doc/src/sgml/Makefile
+++ b/doc/src/sgml/Makefile
@@ -59,7 +59,7 @@ GENERATED_SGML = version.sgml \
 	features-supported.sgml features-unsupported.sgml errcodes-table.sgml \
 	keywords-table.sgml targets-meson.sgml wait_event_types.sgml
 
-ALL_SGML := $(wildcard $(srcdir)/*.sgml $(srcdir)/ref/*.sgml) $(GENERATED_SGML)
+ALL_SGML := $(wildcard $(srcdir)/*.sgml $(srcdir)/ref/*.sgml $(srcdir)/func/*.sgml) $(GENERATED_SGML)
 
 ALL_IMAGES := $(wildcard $(srcdir)/images/*.svg)