diff --git a/src/idl_gen_ts.cpp b/src/idl_gen_ts.cpp
index af0836acf..c7371686b 100644
--- a/src/idl_gen_ts.cpp
+++ b/src/idl_gen_ts.cpp
@@ -1975,7 +1975,8 @@ class TsGenerator : public BaseGenerator {
         GenDocComment(code_ptr);
         code += "static " + namer_.Method("add", field);
         code += "(builder:flatbuffers.Builder, " + argname + ":" +
-                GetArgType(imports, struct_def, field, false) + ") {\n";
+                GetArgType(imports, struct_def, field, /* allow null */ true) +
+                ") {\n";
         code += "  builder.addField" + GenWriteMethod(field.value.type) + "(";
         code += NumToString(it - struct_def.fields.vec.begin()) + ", ";
         if (field.value.type.base_type == BASE_TYPE_BOOL) { code += "+"; }
@@ -1983,11 +1984,7 @@ class TsGenerator : public BaseGenerator {
         if (!IsScalar(field.value.type.base_type)) {
           code += "0";
         } else if (HasNullDefault(field)) {
-          if (IsLong(field.value.type.base_type)) {
-            code += "BigInt(0)";
-          } else {
-            code += "0";
-          }
+          code += "null";
         } else {
           if (field.value.type.base_type == BASE_TYPE_BOOL) { code += "+"; }
           code += GenDefaultValue(field, imports);