diff --git a/nixos/doc/manual/Makefile b/nixos/doc/manual/Makefile
index b251a1f5e2c3..9ff599a0090f 100644
--- a/nixos/doc/manual/Makefile
+++ b/nixos/doc/manual/Makefile
@@ -6,13 +6,14 @@ debug: generated manual-combined.xml
 
 manual-combined.xml: generated *.xml **/*.xml
 	rm -f ./manual-combined.xml
-	nix-shell --packages xmloscopy \
+	nix-shell --pure -Q --packages xmloscopy \
 		--run "xmloscopy --docbook5 ./manual.xml ./manual-combined.xml"
 
 .PHONY: format
 format:
-	find ../../ -iname '*.xml' -type f -print0 | xargs -0 -I{} -n1 \
-		xmlformat --config-file "../xmlformat.conf" -i {}
+	nix-shell --pure -Q --packages xmlformat \
+		--run "find ../../ -iname '*.xml' -type f -print0 | xargs -0 -I{} -n1 \
+		xmlformat --config-file '../xmlformat.conf' -i {}"
 
 .PHONY: fix-misc-xml
 fix-misc-xml: