diff --git a/pkgs/top-level/impure-overlays.nix b/pkgs/top-level/impure-overlays.nix
index a46571d08840..3d0c6831b919 100644
--- a/pkgs/top-level/impure-overlays.nix
+++ b/pkgs/top-level/impure-overlays.nix
@@ -38,7 +38,10 @@ let
       )
     else
       # it's a file, so the result is the contents of the file itself
-      [ (import path) ];
+      let
+        overlay = import path;
+      in
+      if builtins.isFunction overlay then [ overlay ] else overlay;
 in
 if pathOverlays != "" && builtins.pathExists pathOverlays then
   overlays pathOverlays