diff --git a/doc/release-notes/rl-2505.section.md b/doc/release-notes/rl-2505.section.md
index 0e021924848b..20937069624f 100644
--- a/doc/release-notes/rl-2505.section.md
+++ b/doc/release-notes/rl-2505.section.md
@@ -59,3 +59,5 @@
     - `lib.types.listOf`
 
 - Plasma 5 and Qt 5 based versions of associated software are deprecated in NixOS 25.05, and will be removed in NixOS 25.11. Users are encouraged to upgrade to Plasma 6.
+
+- `rustPlatform.buildRustPackage` stops handling the deprecated argument `cargoSha256`. Out-of-tree packages that haven't migrated from `cargoSha256` to `cargoHash` now receive errors.
diff --git a/pkgs/build-support/rust/build-rust-package/default.nix b/pkgs/build-support/rust/build-rust-package/default.nix
index b98fb69b40d9..2f67df349e1d 100644
--- a/pkgs/build-support/rust/build-rust-package/default.nix
+++ b/pkgs/build-support/rust/build-rust-package/default.nix
@@ -83,7 +83,7 @@ lib.extendMkDerivation {
           cargoDeps
         else if cargoLock != null then
           importCargoLock cargoLock
-        else if (args.cargoHash or null == null) && (args.cargoSha256 or null == null) then
+        else if args.cargoHash or null == null then
           throw "cargoHash, cargoVendorDir, cargoDeps, or cargoLock must be set"
         else if useFetchCargoVendor then
           fetchCargoVendor (
@@ -116,15 +116,10 @@ lib.extendMkDerivation {
                 postUnpack
                 cargoUpdateHook
                 ;
+              hash = args.cargoHash;
               name = cargoDepsName;
               patches = cargoPatches;
             }
-            // lib.optionalAttrs (args ? cargoHash) {
-              hash = args.cargoHash;
-            }
-            // lib.optionalAttrs (args ? cargoSha256) {
-              sha256 = lib.warn "cargoSha256 is deprecated. Please use cargoHash with SRI hash instead" args.cargoSha256;
-            }
             // depsExtraArgs
           );