diff --git a/RealmJS.xcodeproj/project.pbxproj b/RealmJS.xcodeproj/project.pbxproj
index 7074fcb2..9ff6dac2 100644
--- a/RealmJS.xcodeproj/project.pbxproj
+++ b/RealmJS.xcodeproj/project.pbxproj
@@ -221,8 +221,8 @@
 				0270BC7B1B7D020100010E03 /* RealmJSTests.mm */,
 				0270BC7C1B7D020100010E03 /* RealmTests.js */,
 				0270BC7D1B7D020100010E03 /* ResultsTests.js */,
-				0270BC7E1B7D020100010E03 /* TestCase.js */,
 				0270BC7F1B7D020100010E03 /* TestObjects.js */,
+				0270BC7E1B7D020100010E03 /* TestCase.js */,
 			);
 			path = RealmJSTests;
 			sourceTree = "<group>";
diff --git a/src/RJSRealm.mm b/src/RJSRealm.mm
index e76206ab..4554686f 100644
--- a/src/RJSRealm.mm
+++ b/src/RJSRealm.mm
@@ -221,7 +221,12 @@ JSValueRef RealmCreateObject(JSContextRef ctx, JSObjectRef function, JSObjectRef
             object = RJSDictForPropertyArray(ctx, object_schema->second, object);
         }
 
-        return RJSObjectCreate(ctx, Object::create<JSValueRef>(ctx, sharedRealm, object_schema->second, object, false));
+        bool update = false;
+        if (argumentCount == 3) {
+            update = RJSValidatedValueToBool(ctx, arguments[2]);
+        }
+
+        return RJSObjectCreate(ctx, Object::create<JSValueRef>(ctx, sharedRealm, object_schema->second, object, update));
     }
     catch (std::exception &exp) {
         if (jsException) {
diff --git a/src/RJSSchema.mm b/src/RJSSchema.mm
index ff836eac..0fba76df 100644
--- a/src/RJSSchema.mm
+++ b/src/RJSSchema.mm
@@ -118,6 +118,7 @@ static inline ObjectSchema RJSParseObjectSchema(JSContextRef ctx, JSObjectRef ob
 
     ObjectSchema objectSchema;
     static JSStringRef nameString = JSStringCreateWithUTF8CString("name");
+
     objectSchema.name = RJSValidatedStringProperty(ctx, objectSchemaObject, nameString);
 
     size_t numProperties = RJSValidatedArrayLength(ctx, propertiesObject);
@@ -126,6 +127,17 @@ static inline ObjectSchema RJSParseObjectSchema(JSContextRef ctx, JSObjectRef ob
         objectSchema.properties.emplace_back(RJSParseProperty(ctx, property));
     }
 
+    static JSStringRef primaryString = JSStringCreateWithUTF8CString("primaryKey");
+    JSValueRef primaryValue = RJSValidatedPropertyValue(ctx, objectSchemaObject, primaryString);
+    if (!JSValueIsUndefined(ctx, primaryValue)) {
+        objectSchema.primary_key = RJSValidatedStringForValue(ctx, primaryValue);
+        Property *property = objectSchema.primary_key_property();
+        if (!property) {
+            throw std::runtime_error("Missing primary key property '" + objectSchema.primary_key + "'");
+        }
+        property->is_primary = true;
+    }
+
     // store prototype
     if (prototypeObject) {
         JSValueProtect(ctx, prototypeObject);
diff --git a/src/RJSUtil.hpp b/src/RJSUtil.hpp
index bf571158..f258325a 100644
--- a/src/RJSUtil.hpp
+++ b/src/RJSUtil.hpp
@@ -112,6 +112,18 @@ static inline double RJSValidatedValueToNumber(JSContextRef ctx, JSValueRef valu
     return number;
 }
 
+static inline bool RJSValidatedValueToBool(JSContextRef ctx, JSValueRef value) {
+    JSValueRef exception = NULL;
+    if (!JSValueIsBoolean(ctx, value)) {
+        throw std::runtime_error("Value is not a boolean");
+    }
+    bool b = JSValueToNumber(ctx, value, &exception);
+    if (exception) {
+        throw RJSException(ctx, exception);
+    }
+    return b;
+}
+
 static inline JSValueRef RJSValidatedPropertyValue(JSContextRef ctx, JSObjectRef object, JSStringRef property) {
     JSValueRef exception = NULL;
     JSValueRef propertyValue = JSObjectGetProperty(ctx, object, property, &exception);
diff --git a/src/object-store/object_accessor.hpp b/src/object-store/object_accessor.hpp
index c7f92022..3e5e3a20 100644
--- a/src/object-store/object_accessor.hpp
+++ b/src/object-store/object_accessor.hpp
@@ -158,7 +158,7 @@ namespace realm {
         size_t row_index = realm::not_found;
         realm::TableRef table = ObjectStore::table_for_object_type(realm->read_group(), object_schema.name);
         Property *primary_prop = object_schema.primary_key_property();
-        if (try_update && primary_prop) {
+        if (primary_prop) {
             // search for existing object based on primary key type
             ValueType primary_value = Accessor::dict_value_for_key(ctx, value, object_schema.primary_key);
             if (primary_prop->type == PropertyTypeString) {
@@ -167,6 +167,10 @@ namespace realm {
             else {
                 row_index = table->find_first_int(primary_prop->table_column, Accessor::to_long(ctx, primary_value));
             }
+
+            if (!try_update && row_index != realm::not_found) {
+                throw std::runtime_error("Attempting to create an object of type '" + object_schema.name + "' with an exising primary key value.");
+            }
         }
 
         // if no existing, create row
diff --git a/tests/RealmTests.js b/tests/RealmTests.js
index 82ce6cf3..82760723 100644
--- a/tests/RealmTests.js
+++ b/tests/RealmTests.js
@@ -82,6 +82,23 @@ var RealmTests = {
         TestCase.assertEqual(objects.length, 2, 'wrong object count');
         TestCase.assertEqual(objects[0].doubleCol, 1, 'wrong object property value');
         TestCase.assertEqual(objects[1].doubleCol, 2, 'wrong object property value');
+
+        // test primary object
+        realm = new Realm({path: TestUtil.realmPathForFile('intPrimary.realm'), schema: [IntPrimaryObjectSchema, StringPrimaryObjectSchema]});
+        realm.write(function() {
+            var obj0 = realm.create('IntPrimaryObject', [0, 'val0']);
+
+            TestCase.assertThrows(function() {
+                realm.create('IntPrimaryObject', [0, 'val0']);
+            });
+            realm.create('IntPrimaryObject', [1, 'val1'], true);
+            var objects = realm.objects('IntPrimaryObject');
+            TestCase.assertEqual(objects.length, 2);
+
+            realm.create('IntPrimaryObject', [0, 'newVal0'], true);
+            TestCase.assertEqual(obj0.valueCol, 'newVal0');
+            TestCase.assertEqual(objects.length, 2);
+        });
     },
 
     testRealmDelete: function() {
@@ -167,3 +184,4 @@ var RealmTests = {
         TestCase.assertEqual(notificationCount, 1);
     },
 };
+
diff --git a/tests/TestObjects.js b/tests/TestObjects.js
index 1154e843..912ccf22 100644
--- a/tests/TestObjects.js
+++ b/tests/TestObjects.js
@@ -58,3 +58,21 @@ var LinkTypesObjectSchema = {
         {name: 'arrayCol',   type: RealmType.Array, objectType: 'TestObject'},
     ]
 };
+
+var IntPrimaryObjectSchema = {
+  name: 'IntPrimaryObject',
+  primaryKey: 'primaryCol',
+  properties: [
+    {name: 'primaryCol', type: RealmType.Int},
+    {name: 'valueCol',   type: RealmType.String},
+  ]
+};
+
+var StringPrimaryObjectSchema = {
+  name: 'StringPrimaryObject',
+  primaryKey: 'primaryCol',
+  properties: [
+    {name: 'primaryCol', type: RealmType.String},
+    {name: 'valueCol',   type: RealmType.String},
+  ]
+};
\ No newline at end of file