diff --git a/app/uk/gov/hmrc/vatapi/models/VatReturn.scala b/app/uk/gov/hmrc/vatapi/models/VatReturn.scala
index fa87d745..2bfdcc20 100644
--- a/app/uk/gov/hmrc/vatapi/models/VatReturn.scala
+++ b/app/uk/gov/hmrc/vatapi/models/VatReturn.scala
@@ -46,7 +46,7 @@ object VatReturn {
       (__ \ "vatDueAcquisitions").read[Amount](vatAmountValidator) and
       (__ \ "totalVatDue").read[Amount](vatAmountValidator) and
       (__ \ "vatReclaimedCurrPeriod").read[Amount](vatAmountValidator) and
-      (__ \ "netVatDue").read[Amount](vatAmountValidator) and
+      (__ \ "netVatDue").read[Amount](vatNonNegativeAmountValidator) and
       (__ \ "totalValueSalesExVAT").read[Amount](vatWholeAmountValidator) and
       (__ \ "totalValuePurchasesExVAT")
         .read[Amount](vatWholeAmountValidator) and
@@ -67,9 +67,9 @@ object VatReturn {
         Validation[VatReturn](
           JsPath \ "netVatDue",
           vatReturn =>
-            vatReturn.netVatDue == vatReturn.totalVatDue - vatReturn.vatReclaimedCurrPeriod,
+            vatReturn.netVatDue == (vatReturn.totalVatDue - vatReturn.vatReclaimedCurrPeriod).abs,
           JsonValidationError(
-            "netVatDue should be equal to totalVatDue - vatReclaimedCurrPeriod",
+            "netVatDue should be the difference between the largest and the smallest values among totalVatDue and vatReclaimedCurrPeriod",
             ErrorCode.VAT_NET_VALUE)
         )
       )
diff --git a/public/api/conf/1.0/application.raml b/public/api/conf/1.0/application.raml
index 4d4003bc..810869ef 100644
--- a/public/api/conf/1.0/application.raml
+++ b/public/api/conf/1.0/application.raml
@@ -144,3 +144,12 @@ traits:
                     description: Invalid request
                     value:
                       code: INVALID_REQUEST
+                  invalidTotalValue:
+                    description: totalVatDue should be equal to the sum of vatDueSales and vatDueAcquisitions
+                    value:
+                      code: VAT_TOTAL_VALUE
+                  invalidNetValue:
+                    description: netVatDue should be the difference between the largest and the smallest values among totalVatDue and vatReclaimedCurrPeriod
+                    value:
+                      code: VAT_NET_VALUE
+
diff --git a/test/uk/gov/hmrc/vatapi/models/VatReturnSpec.scala b/test/uk/gov/hmrc/vatapi/models/VatReturnSpec.scala
index f7c95613..2952d68c 100644
--- a/test/uk/gov/hmrc/vatapi/models/VatReturnSpec.scala
+++ b/test/uk/gov/hmrc/vatapi/models/VatReturnSpec.scala
@@ -59,6 +59,25 @@ class VatReturnSpec extends UnitSpec with JsonSpec {
     )
   }
 
+  "reject VAT returns with negative amounts where non-negative amounts are expected" in {
+    assertValidationErrorWithCode(
+      VatReturn(
+        periodKey = "#001",
+        vatDueSales = 10.00,
+        vatDueAcquisitions = 100.30,
+        totalVatDue = BigDecimal(10.00) + BigDecimal(100.30),
+        vatReclaimedCurrPeriod = 450.00,
+        netVatDue = BigDecimal(10.00) + BigDecimal(100.30) - BigDecimal(450.00),
+        totalValueSalesExVAT = 1000,
+        totalValuePurchasesExVAT = 200.00,
+        totalValueGoodsSuppliedExVAT = 100.00,
+        totalAcquisitionsExVAT = 540.00
+      ),
+      "/netVatDue",
+      ErrorCode.INVALID_MONETARY_AMOUNT
+    )
+  }
+
   "accept VAT returns with negative amounts where non" in {
     assertValidationPasses(
       VatReturn(