diff --git a/pkgs/servers/openafs-client/default.nix b/pkgs/servers/openafs-client/default.nix
index 1d9bd52d912..b5568e6a2ca 100644
--- a/pkgs/servers/openafs-client/default.nix
+++ b/pkgs/servers/openafs-client/default.nix
@@ -34,7 +34,7 @@ stdenv.mkDerivation {
 
     ./regen.sh
 
-    ${optionalString (kerberos != null) ''
+    ${stdenv.lib.optionalString (kerberos != null) ''
       export KRB5_CONFIG=${kerberos}/bin/krb5-config"
     ''}