diff --git a/pkgs/lib/modules.nix b/pkgs/lib/modules.nix
index 286178a0fa7..4c00728a9a5 100644
--- a/pkgs/lib/modules.nix
+++ b/pkgs/lib/modules.nix
@@ -11,17 +11,6 @@ with import ./options.nix;
 with import ./properties.nix;
 
 rec {
-
-  # Unfortunately this can also be a string.
-  isPath = x: !(
-     builtins.isFunction x
-  || builtins.isAttrs x
-  || builtins.isInt x
-  || builtins.isBool x
-  || builtins.isList x
-  );
-
-
   importIfPath = path:
     if isPath path then
       import path
diff --git a/pkgs/lib/trivial.nix b/pkgs/lib/trivial.nix
index 8af3474f2a6..b2304ff7a17 100644
--- a/pkgs/lib/trivial.nix
+++ b/pkgs/lib/trivial.nix
@@ -35,4 +35,14 @@ rec {
     else if builtins.isAttrs x
       then deepSeqAttrs x y
       else seq x y;
+
+  isPath = val: with builtins; !(
+      isAttrs val
+   || isList val
+   || isInt val
+   || isString val
+   || isFunction val
+   || isBool val
+   || val == null
+  );
 }
diff --git a/pkgs/lib/types.nix b/pkgs/lib/types.nix
index 6ddac61d91b..eac76917c2d 100644
--- a/pkgs/lib/types.nix
+++ b/pkgs/lib/types.nix
@@ -96,8 +96,7 @@ rec {
 
     path = mkOptionType {
       name = "path";
-      # Hacky: there is no ‘isPath’ primop.
-      check = lib.traceValIfNot (x: builtins.unsafeDiscardStringContext (builtins.substring 0 1 (toString x)) == "/");
+      check = lib.traceValIfNot isPath;
     };
 
     listOf = types.list;