diff --git a/src/converter.js b/src/converter.js
index 25eed3d45..d375682f8 100644
--- a/src/converter.js
+++ b/src/converter.js
@@ -250,7 +250,7 @@ converter.toObject = function toObject(mtype) {
         ("d%s=o.enums===String?%j:%j", prop, field.resolvedType.valuesById[field.typeDefault], field.typeDefault);
             else if (field.long) gen
         ("if(typeof BigInt!==\"undefined\"&&o.longs===BigInt){")
-            ("d%s=BigInt(%s)", prop, field.typeDefault.toString())
+            ("d%s=BigInt(%j)", prop, field.typeDefault.toString())
         ("}else if(util.Long){")
             ("var n=new util.Long(%i,%i,%j)", field.typeDefault.low, field.typeDefault.high, field.typeDefault.unsigned)
             ("d%s=o.longs===String?n.toString():o.longs===Number?n.toNumber():n", prop)
diff --git a/tests/api_converters.js b/tests/api_converters.js
index b30560ef3..73e0adfff 100644
--- a/tests/api_converters.js
+++ b/tests/api_converters.js
@@ -106,6 +106,7 @@ tape.test("converters", function(test) {
                 var buf = protobuf.util.newBuffer(3);
                 buf[0] = buf[1] = buf[2] = 49; // "111"
                 var msg = Message.create({
+                    // This number was chosen to be > 2^63 and < 2^64
                     uint64Val: protobuf.util.Long.fromString("11000000000000000001", true),
                     uint64Repeated: [2, 3],
                     bytesVal: buf,
@@ -113,6 +114,7 @@ tape.test("converters", function(test) {
                     enumVal: 2,
                     enumRepeated: [1, 100, 2],
                     int64Map: {
+                        // These numbers were chosen to be < Number.MIN_SAFE_INTEGER
                         a: protobuf.util.Long.fromString("-200000000000000001"),
                         b: protobuf.util.Long.fromString("-300000000000000001")
                     }