diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index 255f56b..b7144d9 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -104,7 +104,7 @@ static void generate_orderedappend_paths(PlannerInfo *root, RelOptInfo *rel,
 static Path *get_cheapest_parameterized_child_path(PlannerInfo *root,
 												   RelOptInfo *rel,
 												   Relids required_outer);
-static void accumulate_append_subpath(Path *path,
+static bool accumulate_append_subpath(Path *path,
 									  List **subpaths, List **special_subpaths);
 static Path *get_singleton_append_subpath(Path *path);
 static void set_dummy_rel_pathlist(RelOptInfo *rel);
@@ -1395,8 +1395,14 @@ add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
 		if (childrel->partial_pathlist != NIL)
 		{
 			cheapest_partial_path = linitial(childrel->partial_pathlist);
-			accumulate_append_subpath(cheapest_partial_path,
-									  &partial_subpaths, NULL);
+
+			/*
+			 * Don't allow partial Append if it prevents a child Append from
+			 * being flattened.
+			 */
+			if (!accumulate_append_subpath(cheapest_partial_path,
+										   &partial_subpaths, NULL))
+				partial_subpaths_valid = false;
 		}
 		else
 			partial_subpaths_valid = false;
@@ -2037,8 +2043,10 @@ get_cheapest_parameterized_child_path(PlannerInfo *root, RelOptInfo *rel,
  * children to subpaths and the rest to special_subpaths.  If the latter is
  * NULL, we don't flatten the path at all (unless it contains only partial
  * paths).
+ *
+ * Returns whether able to flatten or not.
  */
-static void
+static bool
 accumulate_append_subpath(Path *path, List **subpaths, List **special_subpaths)
 {
 	if (IsA(path, AppendPath))
@@ -2048,7 +2056,7 @@ accumulate_append_subpath(Path *path, List **subpaths, List **special_subpaths)
 		if (!apath->path.parallel_aware || apath->first_partial_path == 0)
 		{
 			*subpaths = list_concat(*subpaths, apath->subpaths);
-			return;
+			return true;
 		}
 		else if (special_subpaths != NULL)
 		{
@@ -2063,18 +2071,21 @@ accumulate_append_subpath(Path *path, List **subpaths, List **special_subpaths)
 							  apath->first_partial_path);
 			*special_subpaths = list_concat(*special_subpaths,
 											new_special_subpaths);
-			return;
+			return true;
 		}
+		else
+			return false;
 	}
 	else if (IsA(path, MergeAppendPath))
 	{
 		MergeAppendPath *mpath = (MergeAppendPath *) path;
 
 		*subpaths = list_concat(*subpaths, mpath->subpaths);
-		return;
+		return true;
 	}
 
 	*subpaths = lappend(*subpaths, path);
+	return true;
 }
 
 /*