diff --git a/src/dawn_native/metal/ShaderModuleMTL.mm b/src/dawn_native/metal/ShaderModuleMTL.mm
index 82f7096a11..c7dda480a4 100644
--- a/src/dawn_native/metal/ShaderModuleMTL.mm
+++ b/src/dawn_native/metal/ShaderModuleMTL.mm
@@ -61,9 +61,6 @@ namespace dawn_native { namespace metal {
         const VertexState* vertexState,
         std::string* remappedEntryPointName,
         bool* needsStorageBufferLength) {
-        // TODO(crbug.com/tint/256): Set this accordingly if arrayLength(..) is used.
-        *needsStorageBufferLength = false;
-
         ScopedTintICEHandler scopedICEHandler(GetDevice());
 
         std::ostringstream errorStream;
@@ -133,6 +130,8 @@ namespace dawn_native { namespace metal {
                                                          std::move(accessControls),
                                                          /* mayCollide */ true);
 
+        transformInputs.Add<tint::transform::Msl::Config>(kBufferLengthBufferSlot);
+
         tint::Program program;
         tint::transform::DataMap transformOutputs;
         DAWN_TRY_ASSIGN(program, RunTransforms(&transformManager, GetTintProgram(), transformInputs,
@@ -148,6 +147,12 @@ namespace dawn_native { namespace metal {
             return DAWN_VALIDATION_ERROR("Transform output missing renamer data.");
         }
 
+        if (auto* data = transformOutputs.Get<tint::transform::Msl::Result>()) {
+            *needsStorageBufferLength = data->needs_storage_buffer_sizes;
+        } else {
+            return DAWN_VALIDATION_ERROR("Transform output missing MSL data.");
+        }
+
         tint::writer::msl::Generator generator(&program);
         if (!generator.Generate()) {
             errorStream << "Generator: " << generator.error() << std::endl;