diff --git a/src/Functions/FunctionsConversion.h b/src/Functions/FunctionsConversion.h
index 10aa1987559..c732ce5f931 100644
--- a/src/Functions/FunctionsConversion.h
+++ b/src/Functions/FunctionsConversion.h
@@ -2641,7 +2641,7 @@ private:
     WrapperType createMapToMapWrrapper(const DataTypes & from_kv_types, const DataTypes & to_kv_types) const
     {
         return [element_wrappers = getElementWrappers(from_kv_types, to_kv_types), from_kv_types, to_kv_types]
-            (ColumnsWithTypeAndName & arguments, const DataTypePtr &, const ColumnNullable * nullable_source, size_t input_rows_count) -> ColumnPtr
+            (ColumnsWithTypeAndName & arguments, const DataTypePtr &, const ColumnNullable * nullable_source, size_t /*input_rows_count*/) -> ColumnPtr
         {
             const auto * col = arguments.front().column.get();
             const auto & column_map = typeid_cast<const ColumnMap &>(*col);
@@ -2651,7 +2651,7 @@ private:
             for (size_t i = 0; i < 2; ++i)
             {
                 ColumnsWithTypeAndName element = {{nested_data.getColumnPtr(i), from_kv_types[i], ""}};
-                converted_columns[i] = element_wrappers[i](element, to_kv_types[i], nullable_source, input_rows_count);
+                converted_columns[i] = element_wrappers[i](element, to_kv_types[i], nullable_source, (element[0].column)->size());
             }
 
             return ColumnMap::create(converted_columns[0], converted_columns[1], column_map.getNestedColumn().getOffsetsPtr());
@@ -2662,7 +2662,7 @@ private:
     WrapperType createArrayToMapWrrapper(const DataTypes & from_kv_types, const DataTypes & to_kv_types) const
     {
         return [element_wrappers = getElementWrappers(from_kv_types, to_kv_types), from_kv_types, to_kv_types]
-            (ColumnsWithTypeAndName & arguments, const DataTypePtr &, const ColumnNullable * nullable_source, size_t input_rows_count) -> ColumnPtr
+            (ColumnsWithTypeAndName & arguments, const DataTypePtr &, const ColumnNullable * nullable_source, size_t /*input_rows_count*/) -> ColumnPtr
         {
             const auto * col = arguments.front().column.get();
             const auto & column_array = typeid_cast<const ColumnArray &>(*col);
@@ -2672,7 +2672,7 @@ private:
             for (size_t i = 0; i < 2; ++i)
             {
                 ColumnsWithTypeAndName element = {{nested_data.getColumnPtr(i), from_kv_types[i], ""}};
-                converted_columns[i] = element_wrappers[i](element, to_kv_types[i], nullable_source, input_rows_count);
+                converted_columns[i] = element_wrappers[i](element, to_kv_types[i], nullable_source, (element[0].column)->size());
             }
 
             return ColumnMap::create(converted_columns[0], converted_columns[1], column_array.getOffsetsPtr());
diff --git a/tests/queries/0_stateless/01803_const_nullable_map.reference b/tests/queries/0_stateless/01803_const_nullable_map.reference
new file mode 100644
index 00000000000..573541ac970
--- /dev/null
+++ b/tests/queries/0_stateless/01803_const_nullable_map.reference
@@ -0,0 +1 @@
+0
diff --git a/tests/queries/0_stateless/01803_const_nullable_map.sql b/tests/queries/0_stateless/01803_const_nullable_map.sql
new file mode 100644
index 00000000000..4ac9f925e24
--- /dev/null
+++ b/tests/queries/0_stateless/01803_const_nullable_map.sql
@@ -0,0 +1,9 @@
+DROP TABLE IF EXISTS t_map_null;
+
+SET allow_experimental_map_type = 1;
+
+CREATE TABLE t_map_null (a Map(String, String), b String) engine = MergeTree() ORDER BY a;
+INSERT INTO t_map_null VALUES (map('a', 'b', 'c', 'd'), 'foo');
+SELECT count() FROM t_map_null WHERE a = map('name', NULL, '', NULL);
+
+DROP TABLE t_map_null;