diff --git a/app/models/case_log.rb b/app/models/case_log.rb
index aad4d23b0..ef4655a7a 100644
--- a/app/models/case_log.rb
+++ b/app/models/case_log.rb
@@ -55,6 +55,15 @@ class CaseLogValidator < ActiveModel::Validator
     end
   end
 
+  def validate_outstanding_rent_amount(record)
+    if record.outstanding_rent_or_charges == "Yes" && record.outstanding_amount.blank?
+      record.errors.add :outstanding_amount, "You must answer the oustanding amout question if you have outstanding rent or charges."
+    end
+    if record.outstanding_rent_or_charges == "No" && !record.outstanding_amount.blank?
+      record.errors.add :outstanding_amount, "You must not answer the oustanding amout question if you don't have outstanding rent or charges."
+    end
+  end
+
   def validate(record)
     # If we've come from the form UI we only want to validate the specific fields
     # that have just been submitted. If we're submitting a log via API or Bulk Upload
diff --git a/spec/models/case_log_spec.rb b/spec/models/case_log_spec.rb
index 265296e40..aaa7f8c84 100644
--- a/spec/models/case_log_spec.rb
+++ b/spec/models/case_log_spec.rb
@@ -96,6 +96,22 @@ RSpec.describe Form, type: :model do
         }.to raise_error(ActiveRecord::RecordInvalid)
       end
     end
+
+    context "outstanding rent or charges validation" do
+      it "must be anwered if answered yes to outstanding rent or charges" do
+        expect {
+          CaseLog.create!(outstanding_rent_or_charges: "Yes",
+                          outstanding_amount: nil)
+        }.to raise_error(ActiveRecord::RecordInvalid)
+      end
+
+      it "must be not be anwered if answered no to outstanding rent or charges" do
+        expect {
+          CaseLog.create!(outstanding_rent_or_charges: "No",
+                          outstanding_amount: 99)
+        }.to raise_error(ActiveRecord::RecordInvalid)
+      end
+    end
   end
 
   describe "status" do