diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 4c7505e..450da18 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -1788,6 +1788,7 @@ _outIndexOptInfo(StringInfo str, const IndexOptInfo *node)
 	WRITE_BOOL_FIELD(predOK);
 	WRITE_BOOL_FIELD(unique);
 	WRITE_BOOL_FIELD(immediate);
+	WRITE_BOOL_FIELD(allnotnull);
 	WRITE_BOOL_FIELD(hypothetical);
 	/* we don't bother with fields copied from the pg_am entry */
 }
diff --git a/src/backend/optimizer/path/indxpath.c b/src/backend/optimizer/path/indxpath.c
index 606734a..118eb25 100644
--- a/src/backend/optimizer/path/indxpath.c
+++ b/src/backend/optimizer/path/indxpath.c
@@ -950,8 +950,18 @@ build_index_paths(PlannerInfo *root, RelOptInfo *rel,
 	index_is_ordered = (index->sortopfamily != NULL);
 	if (index_is_ordered && pathkeys_possibly_useful)
 	{
+		bool		pathkeys_are_extensible;
+
 		index_pathkeys = build_index_pathkeys(root, index,
 											  ForwardScanDirection);
+		pathkeys_are_extensible = (index->unique &&
+								   index->immediate &&
+								   index->allnotnull &&
+								   index_pathkeys != NIL &&
+								   pathkeys_contained_in(index_pathkeys,
+													root->query_pathkeys));
+		if (pathkeys_are_extensible)
+			index_pathkeys = extend_index_pathkeys(root, rel);
 		useful_pathkeys = truncate_useless_pathkeys(root, rel,
 													index_pathkeys);
 		orderbyclauses = NIL;
diff --git a/src/backend/optimizer/path/pathkeys.c b/src/backend/optimizer/path/pathkeys.c
index 9c8ede6..0df5d46 100644
--- a/src/backend/optimizer/path/pathkeys.c
+++ b/src/backend/optimizer/path/pathkeys.c
@@ -1525,3 +1525,40 @@ has_useful_pathkeys(PlannerInfo *root, RelOptInfo *rel)
 		return true;			/* might be able to use them for ordering */
 	return false;				/* definitely useless */
 }
+
+/*
+ * extend_index_pathkeys
+ *		Build the extended pathkey list from query_pathkeys.
+ */
+List *
+extend_index_pathkeys(PlannerInfo *root, RelOptInfo *rel)
+{
+	List	   *pathkeys = NIL;
+	ListCell   *lc1;
+
+	foreach(lc1, root->query_pathkeys)
+	{
+		PathKey    *pathkey = (PathKey *) lfirst(lc1);
+		bool		found = false;
+		ListCell   *lc2;
+
+		foreach(lc2, pathkey->pk_eclass->ec_members)
+		{
+			EquivalenceMember *member = (EquivalenceMember *) lfirst(lc2);
+
+			if (!bms_equal(member->em_relids, rel->relids))
+				continue;
+			else
+			{
+				pathkeys = lappend(pathkeys, pathkey);
+				found = true;
+				break;
+			}
+		}
+
+		if (!found)
+			break;
+	}
+
+	return pathkeys;
+}
diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c
index 954666c..d45de8f 100644
--- a/src/backend/optimizer/util/plancat.c
+++ b/src/backend/optimizer/util/plancat.c
@@ -333,6 +333,26 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 			info->immediate = index->indimmediate;
 			info->hypothetical = false;
 
+			info->allnotnull = true;
+			for (i = 0; i < ncolumns; i++)
+			{
+				int			attrno = info->indexkeys[i];
+
+				if (attrno == 0)
+				{
+					info->allnotnull = false;
+					break;
+				}
+				else if (attrno > 0)
+				{
+					if (!relation->rd_att->attrs[attrno - 1]->attnotnull)
+					{
+						info->allnotnull = false;
+						break;
+					}
+				}
+			}
+
 			/*
 			 * Estimate the index size.  If it's not a partial index, we lock
 			 * the number-of-tuples estimate to equal the parent table; if it
diff --git a/src/include/nodes/relation.h b/src/include/nodes/relation.h
index 6d7b594..a198d2e 100644
--- a/src/include/nodes/relation.h
+++ b/src/include/nodes/relation.h
@@ -524,6 +524,7 @@ typedef struct IndexOptInfo
 	bool		predOK;			/* true if predicate matches query */
 	bool		unique;			/* true if a unique index */
 	bool		immediate;		/* is uniqueness enforced immediately? */
+	bool		allnotnull;		/* true if index's keys are all not null */
 	bool		hypothetical;	/* true if index doesn't really exist */
 	bool		canreturn;		/* can index return IndexTuples? */
 	bool		amcanorderbyop; /* does AM support order by operator result? */
diff --git a/src/include/optimizer/paths.h b/src/include/optimizer/paths.h
index 999adaa..d62827c 100644
--- a/src/include/optimizer/paths.h
+++ b/src/include/optimizer/paths.h
@@ -196,5 +196,6 @@ extern List *truncate_useless_pathkeys(PlannerInfo *root,
 						  RelOptInfo *rel,
 						  List *pathkeys);
 extern bool has_useful_pathkeys(PlannerInfo *root, RelOptInfo *rel);
+extern List *extend_index_pathkeys(PlannerInfo *root, RelOptInfo *rel);
 
 #endif   /* PATHS_H */
diff --git a/src/test/isolation/expected/drop-index-concurrently-1.out b/src/test/isolation/expected/drop-index-concurrently-1.out
index 75dff56..ab96fa0 100644
--- a/src/test/isolation/expected/drop-index-concurrently-1.out
+++ b/src/test/isolation/expected/drop-index-concurrently-1.out
@@ -19,10 +19,8 @@ Sort
 step explains: EXPLAIN (COSTS OFF) EXECUTE getrow_seq;
 QUERY PLAN     
 
-Sort           
-  Sort Key: id, data
-  ->  Seq Scan on test_dc
-        Filter: ((data)::text = '34'::text)
+Index Scan using test_dc_pkey on test_dc
+  Filter: ((data)::text = '34'::text)
 step select2: SELECT * FROM test_dc WHERE data=34 ORDER BY id,data;
 id             data