diff --git a/lib/types.nix b/lib/types.nix
index 5e9a28ac4f0..0ec94cc5c5e 100644
--- a/lib/types.nix
+++ b/lib/types.nix
@@ -247,6 +247,13 @@ rec {
       merge = mergeEqualOption;
     };
 
+    runtimePath = mkOptionType {
+      name = "runtime path";
+      # Hacky: there is no ‘isPath’ primop.
+      check = x: builtins.substring 0 1 (toString x) == "/";
+      merge = log: defs: mergeEqualOption log (map (attrs: attrs // { value = toString attrs.value; }) defs);
+    };
+
     # drop this in the future:
     list = builtins.trace "`types.list` is deprecated; use `types.listOf` instead" types.listOf;