diff --git a/pkgs/by-name/wx/wxGTK31/package.nix b/pkgs/by-name/wx/wxGTK31/package.nix
index 96d93fe3e942..17b1d60e360f 100644
--- a/pkgs/by-name/wx/wxGTK31/package.nix
+++ b/pkgs/by-name/wx/wxGTK31/package.nix
@@ -89,9 +89,12 @@ stdenv.mkDerivation (finalAttrs: {
     "--enable-webviewwebkit"
   ];
 
-  SEARCH_LIB = lib.optionalString (
-    !stdenv.hostPlatform.isDarwin
-  ) "${libGLU.out}/lib ${libGL.out}/lib ";
+  env = lib.optionalAttrs (!stdenv.hostPlatform.isDarwin) {
+    SEARCH_LIB = toString [
+      "${libGLU.out}/lib"
+      "${libGL.out}/lib"
+    ];
+  };
 
   preConfigure = ''
     substituteInPlace configure --replace \