diff --git a/lib/attrsets.nix b/lib/attrsets.nix
index 9bac69af34f3..2a1b866dbc5e 100644
--- a/lib/attrsets.nix
+++ b/lib/attrsets.nix
@@ -435,9 +435,12 @@ rec {
     useful for deep-overriding.
 
     Example:
-      x = { a = { b = 4; c = 3; }; }
-      overrideExisting x { a = { b = 6; d = 2; }; }
-      => { a = { b = 6; d = 2; }; }
+      overrideExisting {} { a = 1; }
+      => {}
+      overrideExisting { b = 2; } { a = 1; }
+      => { b = 2; }
+      overrideExisting { a = 3; b = 2; } { a = 1; }
+      => { a = 1; b = 2; }
   */
   overrideExisting = old: new:
     mapAttrs (name: value: new.${name} or value) old;