diff --git a/src/Apps/W1/Intrastat/app/src/IntrastatReport/IntrastatReportLine.Table.al b/src/Apps/W1/Intrastat/app/src/IntrastatReport/IntrastatReportLine.Table.al
index 99f1b5b4264..bcf3507ec5b 100644
--- a/src/Apps/W1/Intrastat/app/src/IntrastatReport/IntrastatReportLine.Table.al
+++ b/src/Apps/W1/Intrastat/app/src/IntrastatReport/IntrastatReportLine.Table.al
@@ -94,6 +94,16 @@ table 4812 "Intrastat Report Line"
             Caption = 'Country/Region Code';
             TableRelation = "Country/Region";
             ToolTip = 'Specifies the country/region of the address.';
+            trigger OnValidate()
+            var
+                IntrastatReportMgt: Codeunit IntrastatReportManagement;
+            begin
+                if "Country/Region Code" = '' then begin
+                    Validate("Intrastat Country/Region Code", '');
+                    exit;
+                end;
+
+                Validate("Intrastat Country/Region Code", IntrastatReportMgt.GetIntrastatCodeFromCountryRegion("Country/Region Code"));
         }
         field(8; "Transaction Type"; Code[10])
         {
diff --git a/src/Apps/W1/Intrastat/test/src/IntrastatReportTest.Codeunit.al b/src/Apps/W1/Intrastat/test/src/IntrastatReportTest.Codeunit.al
index 6b482773294..47d286839af 100644
--- a/src/Apps/W1/Intrastat/test/src/IntrastatReportTest.Codeunit.al
+++ b/src/Apps/W1/Intrastat/test/src/IntrastatReportTest.Codeunit.al
@@ -4829,6 +4829,31 @@ codeunit 139550 "Intrastat Report Test"
         Assert.AreEqual(TariffNo."No.", ItemTempl."Tariff No.", '');
     end;
 
+    [Test]
+    procedure ManualIntrastatReportLineUsesIntrastatCode()
+    var
+        CountryRegion: array[2] of Record "Country/Region";
+        IntrastatReportLine: Record "Intrastat Report Line";
+    begin
+        // [SCENARIO 646599] Intrastat Country/Region Code is populated from the Country/Region's Intrastat Code when a line is added manually
+        Initialize();
+
+        // [GIVEN] Create Country/Region with a different Intrastat Code.
+        LibraryIntrastat.CreateCountryRegion(CountryRegion[1], true);
+        LibraryIntrastat.CreateCountryRegion(CountryRegion[2], true);
+        CountryRegion[1].Validate(CountryRegion[1]."Intrastat Code", CountryRegion[2].Code);
+        CountryRegion[1].Modify(true);
+
+        // [GIVEN] An Intrastat Report with a manually added line
+        LibraryIntrastat.CreateIntrastatReportLine(IntrastatReportLine);
+
+        // [WHEN] The Country/Region Code is validated on the line
+        IntrastatReportLine.Validate("Country/Region Code", CountryRegion[1].Code);
+
+        // [THEN] The Intrastat Country/Region Code inherits the Intrastat Code from the Country/Region
+        IntrastatReportLine.TestField("Intrastat Country/Region Code", CountryRegion[2].Code);
+    end;
+
     local procedure Initialize()
     var
         LibraryERMCountryData: Codeunit "Library - ERM Country Data";