diff --git a/contrib/poco b/contrib/poco
index 930a7ec1154..a107b0c9cee 160000
--- a/contrib/poco
+++ b/contrib/poco
@@ -1 +1 @@
-Subproject commit 930a7ec1154f4f9711edfb4b4a39f9fff2a5bbb5
+Subproject commit a107b0c9cee109fe0abfbf509df3c78a1e0c05fa
diff --git a/dbms/src/DataStreams/SummingSortedBlockInputStream.cpp b/dbms/src/DataStreams/SummingSortedBlockInputStream.cpp
index eeda7f50e75..e79366ca02d 100644
--- a/dbms/src/DataStreams/SummingSortedBlockInputStream.cpp
+++ b/dbms/src/DataStreams/SummingSortedBlockInputStream.cpp
@@ -330,7 +330,20 @@ void SummingSortedBlockInputStream::merge(MutableColumns & merged_columns, std::
 
             // Start aggregations with current row
             addRow(current);
-            current_row_is_zero = true;
+
+            if (maps_to_sum.empty())
+            {
+                /// We have only columns_to_aggregate. The status of current row will be determined
+                /// in 'insertCurrentRowIfNeeded' method on the values of aggregate functions.
+                current_row_is_zero = true;
+            }
+            else
+            {
+                /// We have complex maps that will be summed with 'mergeMap' method.
+                /// The single row is considered non zero, and the status after merging with other rows
+                /// will be determined in the branch below (when key_differs == false).
+                current_row_is_zero = false;
+            }
         }
         else
         {
@@ -338,10 +351,8 @@ void SummingSortedBlockInputStream::merge(MutableColumns & merged_columns, std::
 
             // Merge maps only for same rows
             for (const auto & desc : maps_to_sum)
-            {
                 if (mergeMap(desc, current_row, current))
                     current_row_is_zero = false;
-            }
         }
 
         if (!current->isLast())
diff --git a/dbms/tests/queries/0_stateless/00327_summing_composite_nested.sql b/dbms/tests/queries/0_stateless/00327_summing_composite_nested.sql
index 43b37616941..e21389528e4 100644
--- a/dbms/tests/queries/0_stateless/00327_summing_composite_nested.sql
+++ b/dbms/tests/queries/0_stateless/00327_summing_composite_nested.sql
@@ -1,12 +1,7 @@
 DROP TABLE IF EXISTS test.summing_composite_key;
 CREATE TABLE test.summing_composite_key (d Date, k UInt64, FirstMap Nested(k1 UInt32, k2ID Int8, s Float64), SecondMap Nested(k1ID UInt64, k2Key UInt32, k3Type Int32, s Int64)) ENGINE = SummingMergeTree(d, k, 1);
 
-INSERT INTO test.summing_composite_key VALUES ('2000-01-01', 1, [1,2], [3,4], [10,11], [0,1,2], [3,4,5], [-1,-2,-3], [1,10,100]);
-INSERT INTO test.summing_composite_key VALUES ('2000-01-01', 1, [2,1], [4,3], [20,22], [2,2,1], [5,5,0], [-3,-3,-33], [10,100,1000]);
-
-INSERT INTO test.summing_composite_key VALUES ('2000-01-01', 2, [1,2], [3,4], [10,11], [0,1,2], [3,4,5], [-1,-2,-3], [1,10,100]);
-INSERT INTO test.summing_composite_key VALUES ('2000-01-01', 2, [2,1,1], [4,3,3], [20,22,33], [2,2], [5,5], [-3,-3], [10,100]);
-INSERT INTO test.summing_composite_key VALUES ('2000-01-01', 2, [1,2], [3,4], [10,11], [0,1,2], [3,4,5], [-1,-2,-3], [1,10,100]);
+INSERT INTO test.summing_composite_key VALUES ('2000-01-01', 1, [1,2], [3,4], [10,11], [0,1,2], [3,4,5], [-1,-2,-3], [1,10,100]), ('2000-01-01', 1, [2,1], [4,3], [20,22], [2,2,1], [5,5,0], [-3,-3,-33], [10,100,1000]), ('2000-01-01', 2, [1,2], [3,4], [10,11], [0,1,2], [3,4,5], [-1,-2,-3], [1,10,100]), ('2000-01-01', 2, [2,1,1], [4,3,3], [20,22,33], [2,2], [5,5], [-3,-3], [10,100]), ('2000-01-01', 2, [1,2], [3,4], [10,11], [0,1,2], [3,4,5], [-1,-2,-3], [1,10,100]);
 
 SELECT * FROM test.summing_composite_key ORDER BY d, k, _part_index;