diff --git a/lib/serializer/src/SerializerValidation.js b/lib/serializer/src/SerializerValidation.js
index 9aae09f..f0f16a5 100644
--- a/lib/serializer/src/SerializerValidation.js
+++ b/lib/serializer/src/SerializerValidation.js
@@ -109,10 +109,20 @@ var _my = {
         }
 
         this.no_overflow64(value, field_name, unsigned);
+        // BigInteger#isBigInteger https://github.com/cryptocoinjs/bigi/issues/20
+        // (code copied from no_overflow64)
+        if (value.t !== undefined && value.s !== undefined) {
+            value = value.toString();
+        }
         if (typeof value === "number") {
             value = "" + value;
         }
-        return Long.fromString(value, unsigned);
+        value = value.trim();
+        var long_value = Long.fromString(value, unsigned);
+        if (long_value.toString() !== value) {
+            throw new Error(`Unable to safely convert ${field_name} ${value} to long`);
+        }
+        return long_value;
     },
 
     to_string(value, field_name = "") {