diff --git a/doc/src/sgml/Makefile b/doc/src/sgml/Makefile
index a04c532b536..feba0698605 100644
--- a/doc/src/sgml/Makefile
+++ b/doc/src/sgml/Makefile
@@ -156,7 +156,9 @@ XSLTPROC_FO_FLAGS += --stringparam img.src.path '$(srcdir)/'
 	$(XSLTPROC) $(XMLINCLUDE) $(XSLTPROCFLAGS) $(XSLTPROC_FO_FLAGS) --stringparam paper.type USletter -o $@ $^
 
 %.pdf: %.fo $(ALL_IMAGES)
-	$(FOP) -fo $< -pdf $@
+	LANG=C $(FOP) -fo $< -pdf $@ 2>&1 | \
+	awk 'BEGIN { err = 0 }  { print }  /not available in font/ { err = 1 }  END { exit err }' 1>&2  || \
+	(echo "Found characters that cannot be displayed in the PDF document" 1>&2;  exit 1)
 
 
 ##