diff --git a/app/services/bulk_upload/lettings/row_parser.rb b/app/services/bulk_upload/lettings/row_parser.rb
index 1eae1d639..a84e38a26 100644
--- a/app/services/bulk_upload/lettings/row_parser.rb
+++ b/app/services/bulk_upload/lettings/row_parser.rb
@@ -138,6 +138,7 @@ class BulkUpload::Lettings::RowParser
   attribute :field_134, :integer
 
   validates :field_1, presence: true, inclusion: { in: (1..12).to_a }
+  validates :field_4, presence: { if: proc { [1, 3, 5, 7, 9, 11].include?(field_1) } }
 
   def attribute_set
     @attribute_set ||= instance_variable_get(:@attributes)
@@ -158,7 +159,6 @@ class BulkUpload::Lettings::RowParser
 
     log.valid?
 
-
     log.errors.each do |error|
       field = field_for_attribute(error.attribute)
       errors.add(field, error.type)
diff --git a/spec/services/bulk_upload/lettings/row_parser_spec.rb b/spec/services/bulk_upload/lettings/row_parser_spec.rb
index 7a5490c2a..265411f55 100644
--- a/spec/services/bulk_upload/lettings/row_parser_spec.rb
+++ b/spec/services/bulk_upload/lettings/row_parser_spec.rb
@@ -54,6 +54,24 @@ RSpec.describe BulkUpload::Lettings::RowParser do
       end
     end
 
+    describe "#field_4" do
+      context "when nullable permitted" do
+        let(:attributes) { { field_1: "2", field_4: nil } }
+
+        it "can be nulled" do
+          expect(parser.errors[:field_4]).to be_blank
+        end
+      end
+
+      context "when nullable not permitted" do
+        let(:attributes) { { field_1: "1", field_4: nil } }
+
+        it "cannot be nulled" do
+          expect(parser.errors[:field_4]).to be_present
+        end
+      end
+    end
+
     describe "#field_134" do
       context "when an unpermitted value" do
         let(:attributes) { { field_134: 3 } }