diff --git a/HISTORY.md b/HISTORY.md
index e689e70de..eedcc8839 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -6,6 +6,7 @@
 
 ### Fixed
 * Revert recent proxy changes which breaks proxy usage by @andrewdicken-stripe in https://github.com/NetSweet/netsuite/pull/579
+* Handle string field names in `CustomFieldList#respond_to?` (#606)
 
 ### Breaking Changes
 
diff --git a/lib/netsuite/records/custom_field_list.rb b/lib/netsuite/records/custom_field_list.rb
index 193bb4b84..cc7267b4c 100644
--- a/lib/netsuite/records/custom_field_list.rb
+++ b/lib/netsuite/records/custom_field_list.rb
@@ -60,8 +60,8 @@ def method_missing(sym, *args, &block)
         super(sym, *args, &block)
       end
 
-      def respond_to?(sym, include_private = false)
-        return true if @custom_fields_assoc.include?(sym)
+      def respond_to?(method, include_private = false)
+        return true if @custom_fields_assoc.include?(method.to_sym)
         super
       end
 
diff --git a/spec/netsuite/records/custom_field_list_spec.rb b/spec/netsuite/records/custom_field_list_spec.rb
index 2266f51da..5122d0254 100644
--- a/spec/netsuite/records/custom_field_list_spec.rb
+++ b/spec/netsuite/records/custom_field_list_spec.rb
@@ -273,8 +273,14 @@
 
         # field accessors are tested elsewhere, but let's run tests here to check various field types
         expect(list).to respond_to(:custbody_multipleselectfield)
+        expect(list).to respond_to('custbody_multipleselectfield')
         expect(list).to respond_to(:custbody_salesclassification)
+        expect(list).to respond_to('custbody_salesclassification')
         expect(list).to respond_to(:custentity_registeredonline)
+        expect(list).to respond_to('custentity_registeredonline')
+
+        expect(list).to_not respond_to(:non_existant_field)
+        expect(list).to_not respond_to('non_existant_field')
 
         expect(list.to_record).to eql(record)
         expect(list.to_record.length).to eq(1)