diff --git a/lib/types.nix b/lib/types.nix
index ddd37f260c9a..5ffbecda5db3 100644
--- a/lib/types.nix
+++ b/lib/types.nix
@@ -436,10 +436,12 @@ rec {
 
     # Deprecated; should not be used because it quietly concatenates
     # strings, which is usually not what you want.
-    string = separatedString "" // {
-      name = "string";
-      deprecationMessage = "See https://github.com/NixOS/nixpkgs/pull/66346 for better alternative types.";
-    };
+    # We use a lib.warn because `deprecationMessage` doesn't trigger in nested types such as `attrsOf string`
+    string = lib.warn
+      "The type `types.string` is deprecated. See https://github.com/NixOS/nixpkgs/pull/66346 for better alternative types."
+      (separatedString "" // {
+        name = "string";
+      });
 
     passwdEntry = entryType: addCheck entryType (str: !(hasInfix ":" str || hasInfix "\n" str)) // {
       name = "passwdEntry ${entryType.name}";