diff --git a/nixos/lib/utils.nix b/nixos/lib/utils.nix
index 871fbb121d0..40d0854d968 100644
--- a/nixos/lib/utils.nix
+++ b/nixos/lib/utils.nix
@@ -12,6 +12,8 @@ rec {
   toShellPath = shell:
     if types.shellPackage.check shell then
       "/run/current-system/sw${shell.shellPath}"
+    else if types.package.check shell then
+      throw "${shell} is not a shell package"
     else
       shell;
 }
diff --git a/pkgs/os-specific/linux/shadow/default.nix b/pkgs/os-specific/linux/shadow/default.nix
index 7f0d40f6be1..ec3e9b14d2a 100644
--- a/pkgs/os-specific/linux/shadow/default.nix
+++ b/pkgs/os-specific/linux/shadow/default.nix
@@ -53,8 +53,9 @@ stdenv.mkDerivation rec {
   meta = {
     homepage = http://pkg-shadow.alioth.debian.org/;
     description = "Suite containing authentication-related tools such as passwd and su";
-    passthru = {
-      shellPath = "/bin/nologin";
-    };
+  };
+
+  passthru = {
+    shellPath = "/bin/nologin";
   };
 }