diff --git a/lib/strings.nix b/lib/strings.nix
index a05a8ed1c192..3fb5d7994440 100644
--- a/lib/strings.nix
+++ b/lib/strings.nix
@@ -606,8 +606,14 @@ rec {
     :::
   */
   makeSearchPathOutput =
-    output: subDir: pkgs:
-    makeSearchPath subDir (map (lib.getOutput output) pkgs);
+    output:
+    let
+      getOutput' = lib.getOutput output;
+    in
+    subDir: pkgs:
+    concatStringsSep ":" (
+      concatMap (path: if path != null then [ (getOutput' path + "/" + subDir) ] else [ ]) pkgs
+    );
 
   /**
     Construct a library search path (such as RPATH) containing the