diff --git a/src/jrd/par.cpp b/src/jrd/par.cpp
index f2899bcf07..6681bc3287 100644
--- a/src/jrd/par.cpp
+++ b/src/jrd/par.cpp
@@ -1795,6 +1795,9 @@ static void par_partition_by(thread_db* tdbb, CompilerScratch* csb, jrd_nod*& gr
 
 		// We have allocated groupNode with bigger length than expressions. This is to use in
 		// OPT_gen_sort. Now fill that info.
+
+		groupNode->nod_type = nod_sort;
+
 		for (unsigned i = 0; i < count; ++i)
 		{
 			groupNode->nod_arg[count + i * count + i] = (jrd_nod*)(IPTR) false;	// ascending
diff --git a/src/jrd/recsrc/WindowedStream.cpp b/src/jrd/recsrc/WindowedStream.cpp
index facaa770a4..e24747b4c0 100644
--- a/src/jrd/recsrc/WindowedStream.cpp
+++ b/src/jrd/recsrc/WindowedStream.cpp
@@ -208,8 +208,8 @@ namespace
 		  m_outerKeys(outerKeys), m_innerKeys(innerKeys)
 	{
 		fb_assert(m_outer && m_inner && m_innerKeys->nod_count == m_outerKeys->nod_count);
-		fb_assert(m_outerKeys && m_outerKeys->nod_type == nod_list);
-		fb_assert(m_innerKeys && m_innerKeys->nod_type == nod_list);
+		fb_assert(m_outerKeys && (m_outerKeys->nod_type == nod_list || m_outerKeys->nod_type == nod_sort));
+		fb_assert(m_innerKeys && (m_innerKeys->nod_type == nod_list || m_innerKeys->nod_type == nod_sort));
 
 		m_impure = CMP_impure(csb, sizeof(Impure));
 	}