diff --git a/src/jrd/recsrc/SortedStream.cpp b/src/jrd/recsrc/SortedStream.cpp
index 7349d1ab09..ef2ac2b4e9 100644
--- a/src/jrd/recsrc/SortedStream.cpp
+++ b/src/jrd/recsrc/SortedStream.cpp
@@ -268,7 +268,7 @@ Sort* SortedStream::init(thread_db* tdbb) const
 	scb->sort(tdbb);
 
 	// For the sake of prudence, set all record parameter blocks to contain
-	// the most recent format. This will guarentee that all fields mapped
+	// the most recent format. This will guarantee that all fields mapped
 	// back to records by get_sort() have homes in the target record.
 
 	if (records)
@@ -287,7 +287,10 @@ Sort* SortedStream::init(thread_db* tdbb) const
 			stream = item->stream;
 			record_param* const rpb = &request->req_rpb[stream];
 
-			if (rpb->rpb_relation)
+			// dimitr:	I've added the check for !isValid to ensure that we don't overwrite
+			//			the format for an active rpb (i.e. the one having some record fetched).
+			//			See CORE-3806 for example.
+			if (rpb->rpb_relation && !rpb->rpb_number.isValid())
 				VIO_record(tdbb, rpb, MET_current(tdbb, rpb->rpb_relation), tdbb->getDefaultPool());
 		}
 	}