diff --git a/ApplicationLibCode/Commands/CompletionExportCommands/MswExport/RicMswBranchBuilder.cpp b/ApplicationLibCode/Commands/CompletionExportCommands/MswExport/RicMswBranchBuilder.cpp
index 65f1f7f648..b9f4ee7c75 100644
--- a/ApplicationLibCode/Commands/CompletionExportCommands/MswExport/RicMswBranchBuilder.cpp
+++ b/ApplicationLibCode/Commands/CompletionExportCommands/MswExport/RicMswBranchBuilder.cpp
@@ -101,22 +101,13 @@ void applyIcdAreaPerCell( const FishbonesExportContext& context, RigMswWellExpor
 {
     if ( context.icdSegments.empty() ) return;
 
-    std::map<size_t, std::set<int>> icdSegmentsPerCell;
-    for ( const auto& icdSegment : context.icdSegments )
-    {
-        for ( auto globalCellIndex : icdSegment.globalCellIndices )
-        {
-            icdSegmentsPerCell[globalCellIndex].insert( icdSegment.segmentNumber );
-        }
-    }
-
     std::set<int> icdSegmentNumbers;
     for ( const auto& icdSegment : context.icdSegments )
     {
         icdSegmentNumbers.insert( icdSegment.segmentNumber );
     }
 
-    std::map<int, double> areaPerSegment;
+    std::map<int, double> originalAreaPerSegment;
     for ( const auto& branch : exportData.branches )
     {
         for ( const auto& segment : branch.segments )
@@ -124,26 +115,36 @@ void applyIcdAreaPerCell( const FishbonesExportContext& context, RigMswWellExpor
             if ( !segment.wsegvalvData.has_value() ) continue;
             if ( !icdSegmentNumbers.count( segment.segmentNumber ) ) continue;
 
-            areaPerSegment[segment.segmentNumber] = segment.wsegvalvData->area;
+            originalAreaPerSegment[segment.segmentNumber] = segment.wsegvalvData->area;
         }
     }
 
-    // An ICD sub connected to several cells is summed once per cell, in ascending cell order, and
-    // ends up with the sum of the last cell it takes part in. This matches the tree implementation.
-    for ( const auto& [globalCellIndex, segmentNumbers] : icdSegmentsPerCell )
+    // Every sum is computed from the original areas, so the result does not depend on the order the
+    // cells are visited in.
+    std::map<size_t, double> areaSumPerCell;
+    for ( const auto& icdSegment : context.icdSegments )
     {
-        double areaSum = 0.0;
-        for ( auto segmentNumber : segmentNumbers )
+        auto it = originalAreaPerSegment.find( icdSegment.segmentNumber );
+        if ( it == originalAreaPerSegment.end() ) continue;
+
+        for ( auto globalCellIndex : icdSegment.globalCellIndices )
         {
-            auto it = areaPerSegment.find( segmentNumber );
-            if ( it != areaPerSegment.end() ) areaSum += it->second;
+            areaSumPerCell[globalCellIndex] += it->second;
+        }
+    }
+
+    // An ICD sub spans a 0.1 m valve segment and normally connects to a single cell. When it reaches
+    // into more than one, it reports the largest of the sums it takes part in.
+    std::map<int, double> areaPerSegment;
+    for ( const auto& icdSegment : context.icdSegments )
+    {
+        double area = 0.0;
+        for ( auto globalCellIndex : icdSegment.globalCellIndices )
+        {
+            area = std::max( area, areaSumPerCell[globalCellIndex] );
         }
 
-        for ( auto segmentNumber : segmentNumbers )
-        {
-            auto it = areaPerSegment.find( segmentNumber );
-            if ( it != areaPerSegment.end() ) it->second = areaSum;
-        }
+        if ( area > 0.0 ) areaPerSegment[icdSegment.segmentNumber] = area;
     }
 
     for ( auto& branch : exportData.branches )
diff --git a/ApplicationLibCode/Commands/CompletionExportCommands/MswExport/RicMswBranchBuilder.h b/ApplicationLibCode/Commands/CompletionExportCommands/MswExport/RicMswBranchBuilder.h
index 044053f95f..6f14a15a05 100644
--- a/ApplicationLibCode/Commands/CompletionExportCommands/MswExport/RicMswBranchBuilder.h
+++ b/ApplicationLibCode/Commands/CompletionExportCommands/MswExport/RicMswBranchBuilder.h
@@ -108,6 +108,9 @@ void applyEffectiveDiameters( const FishbonesExportContext& context, RigMswWellE
 //--------------------------------------------------------------------------------------------------
 /// Replace the WSEGVALV area of fishbones ICD subs connected to the same grid cell with the sum of
 /// their areas, so that the cell sees the total flow area of the ICDs completing it.
+///
+/// The sums are computed from the original areas only. An ICD sub reaching into more than one cell
+/// reports the largest of the sums it takes part in.
 //--------------------------------------------------------------------------------------------------
 void applyIcdAreaPerCell( const FishbonesExportContext& context, RigMswWellExportData& exportData );
 
diff --git a/ApplicationLibCode/UnitTests/RicMswBranchBuilder-Test.cpp b/ApplicationLibCode/UnitTests/RicMswBranchBuilder-Test.cpp
index 7d1c09b2ef..3fadfb068d 100644
--- a/ApplicationLibCode/UnitTests/RicMswBranchBuilder-Test.cpp
+++ b/ApplicationLibCode/UnitTests/RicMswBranchBuilder-Test.cpp
@@ -354,6 +354,56 @@ TEST( RicMswBranchBuilder, IcdAreaPerCell_SeparateCellsAreIndependent )
     EXPECT_DOUBLE_EQ( 0.003, areaOfSegment( exportData, 20 ) );
 }
 
+//--------------------------------------------------------------------------------------------------
+/// An ICD sub reaching into two cells reports the largest sum, computed from the original areas.
+//--------------------------------------------------------------------------------------------------
+TEST( RicMswBranchBuilder, IcdAreaPerCell_MultipleCellsUseLargestSum )
+{
+    FishbonesExportContext context;
+    context.icdSegments.push_back( { 10, { 100, 200 } } );
+    context.icdSegments.push_back( { 20, { 100 } } );
+    context.icdSegments.push_back( { 30, { 200 } } );
+    context.icdSegments.push_back( { 40, { 200 } } );
+
+    auto exportData = makeExportData( { { 10, 0.001 }, { 20, 0.002 }, { 30, 0.003 }, { 40, 0.004 } } );
+    applyIcdAreaPerCell( context, exportData );
+
+    // Cell 100 sums to 0.003, cell 200 to 0.008. Segment 10 takes part in both and reports the larger.
+    EXPECT_DOUBLE_EQ( 0.008, areaOfSegment( exportData, 10 ) );
+    EXPECT_DOUBLE_EQ( 0.003, areaOfSegment( exportData, 20 ) );
+    EXPECT_DOUBLE_EQ( 0.008, areaOfSegment( exportData, 30 ) );
+    EXPECT_DOUBLE_EQ( 0.008, areaOfSegment( exportData, 40 ) );
+}
+
+//--------------------------------------------------------------------------------------------------
+/// The result does not depend on the order the ICD subs are recorded in.
+//--------------------------------------------------------------------------------------------------
+TEST( RicMswBranchBuilder, IcdAreaPerCell_IsIndependentOfRecordingOrder )
+{
+    FishbonesExportContext forward;
+    forward.icdSegments.push_back( { 10, { 100, 200 } } );
+    forward.icdSegments.push_back( { 20, { 100 } } );
+    forward.icdSegments.push_back( { 30, { 200 } } );
+
+    FishbonesExportContext reversed;
+    reversed.icdSegments.push_back( { 30, { 200 } } );
+    reversed.icdSegments.push_back( { 20, { 100 } } );
+    reversed.icdSegments.push_back( { 10, { 200, 100 } } );
+
+    const std::vector<std::pair<int, double>> segments = { { 10, 0.001 }, { 20, 0.002 }, { 30, 0.003 } };
+
+    auto forwardData = makeExportData( segments );
+    applyIcdAreaPerCell( forward, forwardData );
+
+    auto reversedData = makeExportData( segments );
+    applyIcdAreaPerCell( reversed, reversedData );
+
+    for ( int segmentNumber : { 10, 20, 30 } )
+    {
+        EXPECT_DOUBLE_EQ( areaOfSegment( forwardData, segmentNumber ), areaOfSegment( reversedData, segmentNumber ) );
+    }
+}
+
 //--------------------------------------------------------------------------------------------------
 /// Valve segments that are not fishbones ICD subs are left alone.
 //--------------------------------------------------------------------------------------------------