diff --git a/mdio/dataset_factory.h b/mdio/dataset_factory.h
index cdaa8a3..4f30b9a 100644
--- a/mdio/dataset_factory.h
+++ b/mdio/dataset_factory.h
@@ -183,7 +183,7 @@ absl::Status transform_compressor(nlohmann::json& input /*NOLINT*/,
  */
 void transform_shape(
     nlohmann::json& input /*NOLINT*/, nlohmann::json& variable /*NOLINT*/,
-    std::unordered_map<std::string, int>& dimensionMap /*NOLINT*/) {
+    std::unordered_map<std::string, uint64_t>& dimensionMap /*NOLINT*/) {
   if (input["dimensions"][0].is_object()) {
     nlohmann::json shape = nlohmann::json::array();
     for (auto& dimension : input["dimensions"]) {
@@ -262,7 +262,7 @@ absl::Status transform_metadata(const std::string& path,
  */
 tensorstore::Result<nlohmann::json> from_json_to_spec(
     nlohmann::json& json /*NOLINT*/,
-    std::unordered_map<std::string, int>& dimensionMap /*NOLINT*/,
+    std::unordered_map<std::string, uint64_t>& dimensionMap /*NOLINT*/,
     const std::string& path) {
   nlohmann::json variableStub = R"(
         {
@@ -403,12 +403,18 @@ tensorstore::Result<nlohmann::json> from_json_to_spec(
  * @return A map of dimension names to sizes or error if the dimensions are not
  * consistently sized
  */
-tensorstore::Result<std::unordered_map<std::string, int>> get_dimensions(
+tensorstore::Result<std::unordered_map<std::string, uint64_t>> get_dimensions(
     nlohmann::json& spec /*NOLINT*/) {
-  std::unordered_map<std::string, int> dimensions;
+  std::unordered_map<std::string, uint64_t> dimensions;
   for (auto& variable : spec["variables"]) {
     if (variable["dimensions"][0].is_object()) {
       for (auto& dimension : variable["dimensions"]) {
+        if (dimension["size"].get<uint64_t>() > mdio::constants::kMaxSize) {
+          return absl::InvalidArgumentError(
+              "Dimension " + dimension["name"].dump() +
+              " exceeds maximum size of " +
+              std::to_string(mdio::constants::kMaxSize));
+        }
         if (dimensions.count(dimension["name"]) == 0) {
           dimensions[dimension["name"]] = dimension["size"];
         } else {
@@ -447,7 +453,7 @@ Construct(nlohmann::json& spec /*NOLINT*/, const std::string& path) {
     return dimensions.status();
   }
 
-  std::unordered_map<std::string, int> dimensionMap = dimensions.value();
+  std::unordered_map<std::string, uint64_t> dimensionMap = dimensions.value();
 
   std::vector<nlohmann::json> datasetSpec;
   for (auto& variable : spec["variables"]) {
diff --git a/mdio/dataset_factory_test.cc b/mdio/dataset_factory_test.cc
index 7d6f847..1baf703 100644
--- a/mdio/dataset_factory_test.cc
+++ b/mdio/dataset_factory_test.cc
@@ -607,6 +607,31 @@ TEST(Variable, simple) {
   }
 }
 
+TEST(Variable, maxSizeExceeded) {
+  nlohmann::json j = nlohmann::json::parse(manifest);
+  // Set all Variables to exceed the maximum size
+  j["variables"][0]["dimensions"][0]["size"] = 0x7fffffffffffffff;
+  j["variables"][0]["dimensions"][1]["size"] = 0x7fffffffffffffff;
+  j["variables"][1]["dimensions"][0]["size"] = 0x7fffffffffffffff;
+  j["variables"][2]["dimensions"][0]["size"] = 0x7fffffffffffffff;
+
+  auto res = Construct(j, "zarrs/simple_dataset");
+  ASSERT_FALSE(res.status().ok())
+      << "Construction succeeded despite exceeding maximum size";
+}
+
+TEST(Variable, maxSizeReached) {
+  nlohmann::json j = nlohmann::json::parse(manifest);
+  // Set all Variables to reach the maximum size
+  j["variables"][0]["dimensions"][0]["size"] = mdio::constants::kMaxSize;
+  j["variables"][0]["dimensions"][1]["size"] = mdio::constants::kMaxSize;
+  j["variables"][1]["dimensions"][0]["size"] = mdio::constants::kMaxSize;
+  j["variables"][2]["dimensions"][0]["size"] = mdio::constants::kMaxSize;
+
+  auto res = Construct(j, "zarrs/simple_dataset");
+  ASSERT_TRUE(res.status().ok()) << res.status();
+}
+
 TEST(Xarray, open) {
   nlohmann::json j = nlohmann::json::parse(manifest);
   auto res = Construct(j, "zarrs/simple_dataset");
diff --git a/mdio/impl.h b/mdio/impl.h
index 4d48f71..c019186 100644
--- a/mdio/impl.h
+++ b/mdio/impl.h
@@ -114,6 +114,9 @@ constexpr auto kCreateClean =
 /// Create a new file or error if it already exists.
 constexpr auto kCreate = tensorstore::OpenMode::create;
 
+// Tensorstore appears to be imposing a max size of 0x3fffffffffffffff
+constexpr uint64_t kMaxSize = 4611686018427387903;
+
 // Supported dtypes
 constexpr auto kBool = tensorstore::dtype_v<mdio::dtypes::bool_t>;
 constexpr auto kInt8 = tensorstore::dtype_v<mdio::dtypes::int8_t>;