diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5f2d7693..dd3110cf 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,7 @@
 - Handles an emtpy tensor for convolution (issue #384)
 - When `coordinates` is provided in `MinkowskiToSparseTensor`, `remove_zeros` will be ignored (issue #387)
 - Pybind equality error from the package (issue #414)
+- Fix undefined coordinate merge for multiple coordinate unions
 
 ## [0.5.4]
 
diff --git a/src/coordinate_map_manager.cpp b/src/coordinate_map_manager.cpp
index 8f67fb8d..d24d95b6 100644
--- a/src/coordinate_map_manager.cpp
+++ b/src/coordinate_map_manager.cpp
@@ -1265,7 +1265,8 @@ CoordinateMapManager<coordinate_type, coordinate_field_type, TemplatedAllocator,
   }
 
   // Create a merged map with the smallest tensor stride
-  coordinate_map_key_type merged_map_key(merged_map_tensor_stride, "merge");
+  coordinate_map_key_type merged_map_key =
+      get_random_string_id(merged_map_tensor_stride, "merge");
   map_type const &map = m_coordinate_maps.find(map_keys[0])->second;
   map_type merged_map = map.merge(maps);
   insert(merged_map_key, merged_map);