diff --git a/src/dawn_native/null/DeviceNull.cpp b/src/dawn_native/null/DeviceNull.cpp
index adc44f0974..fd91585faf 100644
--- a/src/dawn_native/null/DeviceNull.cpp
+++ b/src/dawn_native/null/DeviceNull.cpp
@@ -209,8 +209,8 @@ namespace dawn_native { namespace null {
         return {};
     }
 
-    MaybeError Device::IncrementMemoryUsage(size_t bytes) {
-        static_assert(kMaxMemoryUsage <= std::numeric_limits<size_t>::max() / 2, "");
+    MaybeError Device::IncrementMemoryUsage(uint64_t bytes) {
+        static_assert(kMaxMemoryUsage <= std::numeric_limits<size_t>::max(), "");
         if (bytes > kMaxMemoryUsage || mMemoryUsage + bytes > kMaxMemoryUsage) {
             return DAWN_OUT_OF_MEMORY_ERROR("Out of memory.");
         }
@@ -218,7 +218,7 @@ namespace dawn_native { namespace null {
         return {};
     }
 
-    void Device::DecrementMemoryUsage(size_t bytes) {
+    void Device::DecrementMemoryUsage(uint64_t bytes) {
         ASSERT(mMemoryUsage >= bytes);
         mMemoryUsage -= bytes;
     }
diff --git a/src/dawn_native/null/DeviceNull.h b/src/dawn_native/null/DeviceNull.h
index f6f361185c..56cb6a82dc 100644
--- a/src/dawn_native/null/DeviceNull.h
+++ b/src/dawn_native/null/DeviceNull.h
@@ -106,8 +106,8 @@ namespace dawn_native { namespace null {
                                            uint64_t destinationOffset,
                                            uint64_t size) override;
 
-        MaybeError IncrementMemoryUsage(size_t bytes);
-        void DecrementMemoryUsage(size_t bytes);
+        MaybeError IncrementMemoryUsage(uint64_t bytes);
+        void DecrementMemoryUsage(uint64_t bytes);
 
       private:
         using DeviceBase::DeviceBase;
@@ -147,7 +147,7 @@ namespace dawn_native { namespace null {
 
         std::vector<std::unique_ptr<PendingOperation>> mPendingOperations;
 
-        static constexpr size_t kMaxMemoryUsage = 256 * 1024 * 1024;
+        static constexpr uint64_t kMaxMemoryUsage = 256 * 1024 * 1024;
         size_t mMemoryUsage = 0;
     };