diff --git a/lib/session/MeasurementSession.h b/lib/session/MeasurementSession.h
index 0924662..0cc15fa 100644
--- a/lib/session/MeasurementSession.h
+++ b/lib/session/MeasurementSession.h
@@ -92,7 +92,10 @@ private:
                 "serializeChunk: invalid startIdx" );
 
         if( startIdx >= currentChunk->getStartIndex() ) {
-            encoder.sendArrayPartialContents( currentChunk->getDataPointer(), currentChunk->numMeasurements() );
+            const auto localStartIdx = startIdx - currentChunk->getStartIndex();
+            const auto numElements = currentChunk->numMeasurements() - localStartIdx;
+            assert(numElements <= currentChunk->numMeasurements(), "Internal problem in serializeChunk");
+            encoder.sendArrayPartialContents( currentChunk->getDataPointer() + localStartIdx, numElements );
             return currentChunk->getStartIndex() + currentChunk->numMeasurements();
         } else if( startIdx >= otherChunk->getStartIndex() && otherChunkFilled() ) {
             encoder.sendArrayPartialContents( otherChunk->getDataPointer(), otherChunk->numMeasurements() );