diff --git a/pkgs/build-support/rust/build-rust-package/default.nix b/pkgs/build-support/rust/build-rust-package/default.nix
index 95b6f357e56a..db0d2c53bb1e 100644
--- a/pkgs/build-support/rust/build-rust-package/default.nix
+++ b/pkgs/build-support/rust/build-rust-package/default.nix
@@ -52,8 +52,9 @@
 , buildAndTestSubdir ? null
 , ... } @ args:
 
-assert cargoVendorDir == null && cargoLock == null -> !(args ? cargoSha256) && !(args ? cargoHash)
-  -> throw "cargoSha256, cargoHash, cargoVendorDir, or cargoLock must be set";
+assert cargoVendorDir == null && cargoLock == null
+    -> !(args ? cargoSha256 && args.cargoSha256 != null) && !(args ? cargoHash && args.cargoHash != null)
+    -> throw "cargoSha256, cargoHash, cargoVendorDir, or cargoLock must be set";
 assert buildType == "release" || buildType == "debug";
 
 let