diff --git a/src/AggregateFunctions/AggregateFunctionDeltaSum.h b/src/AggregateFunctions/AggregateFunctionDeltaSum.h
index 99406618da5..33bc2ea99d8 100644
--- a/src/AggregateFunctions/AggregateFunctionDeltaSum.h
+++ b/src/AggregateFunctions/AggregateFunctionDeltaSum.h
@@ -79,7 +79,7 @@ public:
             place_data->sum += rhs_data->sum + (rhs_data->first - place_data->last);
             place_data->last = rhs_data->last;
         }
-        else if ((rhs_data->last < place_data->first && rhs_data->seen_last && place_data->seen_first))
+        else if ((rhs_data->first < place_data->last && rhs_data->seen_last && place_data->seen_first))
         {
             // In the opposite scenario, the lhs comes after the rhs, e.g. [4, 6] [1, 2]. Since we
             // assume the input interval states are sorted by time, we assume this is a counter
@@ -87,9 +87,9 @@ public:
             // rhs last value.
 
             place_data->sum += rhs_data->sum;
-            place_data->first = rhs_data->first;
+            place_data->last = rhs_data->last;
         }
-        else if (rhs_data->seen_first)
+        else if (rhs_data->seen_first && !place_data->seen_first)
         {
             // If we're here then the lhs is an empty state and the rhs does have some state, so
             // we'll just take that state.
diff --git a/tests/queries/0_stateless/01700_deltasum.reference b/tests/queries/0_stateless/01700_deltasum.reference
index be5b176c627..6be953e2b2d 100644
--- a/tests/queries/0_stateless/01700_deltasum.reference
+++ b/tests/queries/0_stateless/01700_deltasum.reference
@@ -7,3 +7,4 @@
 2
 2.25
 6.5
+7
diff --git a/tests/queries/0_stateless/01700_deltasum.sql b/tests/queries/0_stateless/01700_deltasum.sql
index 93edb2e477d..83d5e0439d2 100644
--- a/tests/queries/0_stateless/01700_deltasum.sql
+++ b/tests/queries/0_stateless/01700_deltasum.sql
@@ -7,3 +7,4 @@ select deltaSumMerge(rows) from (select deltaSumState(arrayJoin([0, 1])) as rows
 select deltaSumMerge(rows) from (select deltaSumState(arrayJoin([4, 5])) as rows union all select deltaSumState(arrayJoin([0, 1])) as rows);
 select deltaSum(arrayJoin([2.25, 3, 4.5]));
 select deltaSumMerge(rows) from (select deltaSumState(arrayJoin([0.1, 0.3, 0.5])) as rows union all select deltaSumState(arrayJoin([4.1, 5.1, 6.6])) as rows);
+select deltaSumMerge(rows) from (select deltaSumState(arrayJoin([3, 5])) as rows union all select deltaSumState(arrayJoin([1, 2])) as rows union all select deltaSumState(arrayJoin([4, 6])) as rows);