diff --git a/ujson/src/ujson/Value.scala b/ujson/src/ujson/Value.scala
index bf7507687..15dbcb22f 100644
--- a/ujson/src/ujson/Value.scala
+++ b/ujson/src/ujson/Value.scala
@@ -180,7 +180,9 @@ object Value extends AstTransformer[Value]{
 
   override def visitFloat64StringParts(s: CharSequence, decIndex: Int, expIndex: Int, index: Int) = {
     ujson.Num(
-      if (decIndex != -1 || expIndex != -1) s.toString.toDouble
+      if (decIndex != -1 || expIndex != -1 || s.length() >= 19 /*digit count of largest positive long*/) {
+        s.toString.toDouble
+      }
       else ParseUtils.parseIntegralNum(s, decIndex, expIndex, index).toDouble
     )
   }
diff --git a/ujson/test/src/ujson/SmallJsonTests.scala b/ujson/test/src/ujson/SmallJsonTests.scala
index 11fd25eaa..f06ac1fa9 100644
--- a/ujson/test/src/ujson/SmallJsonTests.scala
+++ b/ujson/test/src/ujson/SmallJsonTests.scala
@@ -23,6 +23,50 @@ object SmallJsonTests extends TestSuite {
 
       }
     }
+    test("largeDouble"){
+      test("longMaxValue") {
+        assert(
+          ujson.read("9223372036854775807").num ==
+          "9223372036854775807".toDouble
+        )
+      }
+      test("longMinValue") {
+        assert(
+          ujson.read("-9223372036854775808").num ==
+          "-9223372036854775808".toDouble
+        )
+      }
+      test("longMaxValuePlusOne") {
+        assert(
+          ujson.read("9223372036854775808").num ==
+          "9223372036854775808".toDouble
+        )
+      }
+      test("longMinValueMinusOne") {
+        assert(
+          ujson.read("-9223372036854775809").num ==
+          "-9223372036854775809".toDouble
+        )
+      }
+      test("issue240"){
+        assert(
+          ujson.read("28291041994989161181883157038606177750").num ==
+            "28291041994989161181883157038606177750".toDouble
+        )
+      }
+      test("largeDecimalPoint"){
+        assert(
+          ujson.read("28291041994989161181883157038606177750.28291041994989161181883157038606177750").num ==
+            "28291041994989161181883157038606177750.28291041994989161181883157038606177750".toDouble
+        )
+      }
+      test("largeDecimalPointExponent"){
+        assert(
+          ujson.read("28291041994989161181883157038606177750.28291041994989161181883157038606177750E123456789").num ==
+            "28291041994989161181883157038606177750.28291041994989161181883157038606177750E123456789".toDouble
+        )
+      }
+    }
     test("inputsEu"){
       TestUtil.checkParse(
         """{