diff --git a/lib/smalloc.js b/lib/smalloc.js
index 9ebbaf402d17df..f181cb60cf2d7c 100644
--- a/lib/smalloc.js
+++ b/lib/smalloc.js
@@ -2,6 +2,8 @@
 
 const smalloc = process.binding('smalloc');
 const kMaxLength = smalloc.kMaxLength;
+const kMinType = smalloc.kMinType;
+const kMaxType = smalloc.kMaxType;
 const util = require('util');
 
 exports.alloc = alloc;
@@ -15,24 +17,8 @@ Object.defineProperty(exports, 'kMaxLength', {
   enumerable: true, value: kMaxLength, writable: false
 });
 
-// enumerated values for different external array types
-var Types = {};
-
-// Must match enum v8::ExternalArrayType.
-Object.defineProperties(Types, {
-  'Int8': { enumerable: true, value: 1, writable: false },
-  'Uint8': { enumerable: true, value: 2, writable: false },
-  'Int16': { enumerable: true, value: 3, writable: false },
-  'Uint16': { enumerable: true, value: 4, writable: false },
-  'Int32': { enumerable: true, value: 5, writable: false },
-  'Uint32': { enumerable: true, value: 6, writable: false },
-  'Float': { enumerable: true, value: 7, writable: false },
-  'Double': { enumerable: true, value: 8, writable: false },
-  'Uint8Clamped': { enumerable: true, value: 9, writable: false }
-});
-
 Object.defineProperty(exports, 'Types', {
-  enumerable: true, value: Types, writable: false
+  enumerable: true, value: Object.freeze(smalloc.types), writable: false
 });
 
 
@@ -59,8 +45,7 @@ function alloc(n, obj, type) {
   if (smalloc.hasExternalData(obj))
     throw new TypeError('object already has external array data');
 
-  // 1 == v8::kExternalUint8Array, 9 == v8::kExternalUint8ClampedArray
-  if (type < 1 || type > 9)
+  if (type < kMinType || type > kMaxType)
     throw new TypeError('unknown external array type: ' + type);
   if (n > kMaxLength)
     throw new RangeError('Attempt to allocate array larger than maximum ' +
diff --git a/src/smalloc.cc b/src/smalloc.cc
index 834b93a7473dd1..319c3937605404 100644
--- a/src/smalloc.cc
+++ b/src/smalloc.cc
@@ -10,6 +10,20 @@
 #include <string.h>
 
 #define ALLOC_ID (0xA10C)
+#define EXTERNAL_ARRAY_TYPES(V)                                               \
+  V(Int8, kExternalInt8Array)                                                 \
+  V(Uint8, kExternalUint8Array)                                               \
+  V(Int16, kExternalInt16Array)                                               \
+  V(Uint16, kExternalUint16Array)                                             \
+  V(Int32, kExternalInt32Array)                                               \
+  V(Uint32, kExternalUint32Array)                                             \
+  V(Float, kExternalFloat32Array)                                             \
+  V(Double, kExternalFloat64Array)                                            \
+  V(Uint8Clamped, kExternalUint8ClampedArray)
+
+#define MIN(a, b) ((a) < (b) ? (a) : (b))
+#define MAX(a, b) ((a) > (b) ? (a) : (b))
+
 
 namespace node {
 namespace smalloc {
@@ -559,6 +573,7 @@ void Initialize(Handle<Object> exports,
                 Handle<Value> unused,
                 Handle<Context> context) {
   Environment* env = Environment::GetCurrent(context);
+  Isolate* isolate = env->isolate();
 
   env->SetMethod(exports, "copyOnto", CopyOnto);
   env->SetMethod(exports, "sliceOnto", SliceOnto);
@@ -573,6 +588,25 @@ void Initialize(Handle<Object> exports,
   exports->Set(FIXED_ONE_BYTE_STRING(env->isolate(), "kMaxLength"),
                Uint32::NewFromUnsigned(env->isolate(), kMaxLength));
 
+  Local<Object> types = Object::New(isolate);
+
+  uint32_t kMinType = ~0;
+  uint32_t kMaxType = 0;
+  #define V(name, value)                                                      \
+    types->Set(FIXED_ONE_BYTE_STRING(env->isolate(), #name),                  \
+                Uint32::NewFromUnsigned(env->isolate(), v8::value));          \
+    kMinType = MIN(kMinType, v8::value);                                      \
+    kMaxType = MAX(kMinType, v8::value);
+
+    EXTERNAL_ARRAY_TYPES(V)
+  #undef V
+
+  exports->Set(FIXED_ONE_BYTE_STRING(env->isolate(), "types"), types);
+  exports->Set(FIXED_ONE_BYTE_STRING(env->isolate(), "kMinType"),
+               Uint32::NewFromUnsigned(env->isolate(), kMinType));
+  exports->Set(FIXED_ONE_BYTE_STRING(env->isolate(), "kMaxType"),
+               Uint32::NewFromUnsigned(env->isolate(), kMaxType));
+
   HeapProfiler* heap_profiler = env->isolate()->GetHeapProfiler();
   heap_profiler->SetWrapperClassInfoProvider(ALLOC_ID, WrapperInfo);
 }
diff --git a/test/parallel/test-smalloc.js b/test/parallel/test-smalloc.js
index 61ffe3b84da88c..ef1aa60bad6838 100644
--- a/test/parallel/test-smalloc.js
+++ b/test/parallel/test-smalloc.js
@@ -309,3 +309,23 @@ assert.throws(function() {
 assert.throws(function() {
   smalloc.dispose({});
 });
+
+
+// Types should be immutable
+assert.deepStrictEqual(Object.getOwnPropertyDescriptor(smalloc, 'Types'), {
+  value: smalloc.Types,
+  writable: false,
+  enumerable: true,
+  configurable: false
+});
+
+var types = Object.keys(smalloc.Types);
+var Types = smalloc.Types;
+
+for (var i = 0; i < types.length; i++)
+  assert.deepStrictEqual(Object.getOwnPropertyDescriptor(Types, types[i]), {
+    value: Types[types[i]],
+    writable: false,
+    enumerable: true,
+    configurable: false
+  });