diff --git a/pkgs/development/libraries/science/math/cudnn/generic.nix b/pkgs/development/libraries/science/math/cudnn/generic.nix
index 731b5588f887..1a798ad704a2 100644
--- a/pkgs/development/libraries/science/math/cudnn/generic.nix
+++ b/pkgs/development/libraries/science/math/cudnn/generic.nix
@@ -21,12 +21,12 @@
 
 { fullVersion
 , url
-, hash ? null
-, sha256 ? null
+, hash ? ""
+, sha256 ? ""
 , supportedCudaVersions ? [ ]
 }:
 
-assert (hash != null) || (sha256 != null);
+assert (hash != "") || (sha256 != "");
 
 assert useCudatoolkitRunfile || (libcublas != null);