diff --git a/Makefile b/Makefile
index 0a9b4f29f..f25830789 100644
--- a/Makefile
+++ b/Makefile
@@ -102,7 +102,13 @@ ifneq ($(ssh),)
 populate: populate-flags += --ssh=$(ssh)
 endif
 populate:
-	$(call evaluate,config.krebs.build.source) --json --strict | \
+	nix-instantiate \
+		--eval \
+		--json \
+		--readonly-mode \
+		--show-trace \
+		--strict \
+		$(LOGNAME)/1systems/$(system)/source.nix | \
 	populate $(populate-target) $(populate-flags)
 
 # usage: make pkgs.populate
diff --git a/krebs/4lib/infest/prepare.sh b/krebs/4lib/infest/prepare.sh
index 50d521e17..d39aca348 100644
--- a/krebs/4lib/infest/prepare.sh
+++ b/krebs/4lib/infest/prepare.sh
@@ -102,7 +102,7 @@ prepare_nixos_iso() {
   mkdir -p bin
   rm -f bin/nixos-install
   cp "$(type -p nixos-install)" bin/nixos-install
-  sed -i "s@^NIX_PATH=\"[^\"]*\"@NIX_PATH=$target_path@" bin/nixos-install
+  sed -i "s@NIX_PATH=\"[^\"]*\"@NIX_PATH=$target_path@" bin/nixos-install
 }
 
 get_nixos_install() {